AU657014B2

AU657014B2 - Durable low-emissivity solar control thin film coating

Info

Publication number: AU657014B2
Application number: AU29890/92A
Authority: AU
Inventors: Abraham I. Belkind; Ronald E Laird; Jesse D. Wolfe
Original assignee: BOC Group Inc
Current assignee: Messer LLC
Priority date: 1992-03-04
Filing date: 1992-12-04
Publication date: 1995-02-23
Anticipated expiration: 2012-12-04
Also published as: CA2084537A1; EP0560534A1; FI930941A7; TW221703B; FI930941A0; KR930020179A; NO924849L; NO924849D0; AU2989092A; JPH063523A; MX9300283A

Description

657014

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): The BOC Group, Inc.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Durable low-emissivity solar control thin film coating r r r r r

S

The following statement is a full description of of performing it known to me/us:this invention, including the best method

T

f la 0000 Background of the Invention This invention relates generally to visibly 10 transparent infrared reflecting interference filters, and more particularly, to a durable low-emissivity filter.

0" The use of transparent panels in buildings, vehicles and other structures for controlling solar 15 radiation is quite prevalent today. The goal of solar control is to transmit light while excluding much of the solar energy, thus decreasing the amount of air 0. condition or cooling required, and conserving energy.

In addition, modified glass as a structural material provides the color flexibility architects desire.

Various processes have been employed to alter the optical pioperties of these panels, including coating glass or plastic substrates by various techniques such as electrolysis, chemical vapor deposition and physical vapor deposition, including sputtering with planar magnetrons. For instance, thin metal films have been deposited on glass or plastic to increase the reflectance of solar radiation. Windows deposited with a multi-layer dielectric-metal-dielectric -2coating that exhibits high visible transmittance, and high reflectivity and low emissivity in the infrared range, are even more energy efficient. The index of refraction of the dielectric layer is preferably 2.0 or greater in order to minimise the visible reflectance and enhance the visible transmittance of the window. This dielectric layer which often consists of metal oxide coating also offers additional protection to the fragile metal films. The optical properties of panels can also be modified by altering the composition of the substrate material. Nevertheless, interference filter panels manufactured by the abovedescribed methods have been only partially successful in reflecting solar radiation to the degree required for significant energy conservation. For example, Apfel et al., U.S. Patent 3,682,528, issued August 8, 1972, described an infra-red interference filter with visible light transmission ge of only approximately 72% and with infra-red transmission of approximately 8%.

20 Summary of the Invention According to the present invention there is provided a thin film interference filter comprising: a transparent substrate; a first dielectric layer; a first metal pr \coat layer; a partially refl-, tive metal layer; a second metal precoat layer; and a second dielectric layer e in which one of the dielectric layers is a composite comprising a mixture of silicon nitride and one or more of zirconium nitride, titanium, nitride, and hafnium nitride.

arther according to the present invention there is pro\.ded a method for the production of a thin film interference filter on a transparent substrate, with the filter having a substantially neutral visible reflected colour, comprising the steps, in sequence, of: reactively sputtering a first substantially transparent dielectric layer onto said substrate; Sdepositing a first metal precoat layer; depositing a partially reflective metal layer; 94Il29,p:opr\phh2989-92-333,2 -3depositing a second metal precoat layer; and reactively sputtering onto said second metal precoat layer a second substantially transparent dielectric layer comprising a composite of silicon nitride and one or more of zirconium nitride, titanium nitride, and hafnium nitride.

The thin-film interference filter of the invention comprises a substrate onto which is deposited a dielectric layer, followed by metal and dielectric layers. In between each dielectric layer and the metal layer is deposited a "nucleation" or glue layer that promotes adhesion between the dielectric and the metal. In one preferred embodiment, the interference filter comprises a five layer structure wherein one or both of the dielectric layers is formed of a composite material containing zirconium nitride and silicon nitride.

It was found that mixing zirconium nitride with silicon nitride creates a composite layer that has a high refractive index and excellent transparency in the visible region.

Moreover, the optical properties of this composite layer can 20 be adjusted by varying the relative amounts of zirconium nitride and silicon nitride.

The dielectric layers of the inventive interferences filters can be reactively sputtered by a rotatable cylindrical magnetron. Composite layers can be formed by 25 cosputtering from dual cathode targets or from one or more alloy targets. An advantage of the inventive process is that •by reducing the intrinsic stress of the second dielectric !layer, an extremely hard and chemically resistant thin film coating is produced. In sputtering silicon nitride for the second dielectric layer, it was demonstrated that the intrinsic stress of this layer can be reduced by orienting the magnetic assembly of the cathode at an acute angle vis-avis the substrate.

Additional objects, advantages and features of the present invention will become apparent from the following detailed exemplary description, which description should be taken in conjunction with the accompanying drawings.

941129,p:\oper\phh,989O.9Z333,3 Brief Description of the Drawings Figure la is a cross-sectional view of a five layer design thin-film interference filter produced in accordance with this invention.

Figure Ib is a graph illustrating the spectral transmittance and reflectance of a thin-film interference filter. Figure 2 is a cross-sectional view of a cathode assembly.

Figure 3 is a graph illustrating the spectral transmission in the visible light region for a composite film.

Figure 4 is a graph illustrating the spectral reflection in the visible light region for a composite film.

Figure 5 is a graph illustrating the spectral adsorption in the visible light region for a composite film.

Description of the Preferred Embodiments A thin-film interference filter incorporating the present invention is shown in Figure la. As shown therein, the filter consists of a transparent substrate 2 which is provided with two planar parallel surfaces 4 and 6, in which surface 4 is exposed to the medium and :5 surface 6 is coated. The substrate can be formed of any suitable transparent material; however, the substrate is preferably a material which has superior structural properties and minimum absorption in the visible and near-infrared spectra regions where the solar energy is concentrated. Crystalline quartz, fused silica, sodalime silicate glass, and plastics such as polycarbonates and acrylates, are all preferred substrate materials.

S1, Deposited onto the substrate surface 6 is a 3 first dielectric layer 8 that is preferably made of a 35 material having an index of refraction of greater than about 2.0, and most preferably between 2.4 and 2.7.

Suitable dielectric layer materials include metal oxides such as titanium oxide, tin oxide, zinc oxide, indium oxide (optionally doped with tin oxide), bismuth oxide, and zirconium oxide. See Hart, U.S. Patent 4,462,883, issued July 31, 1984, which is incorporated herein by reference. Yet another suitable material is silicon nitride. A particularly suitable dielectric material comprises a thin composite film containing zirconium nitride and silicon nitride (collectively referred to herein as "SiZrN") that is fabricated by cosputtering from dual targets or from a single alloy target of a dc cylindrical magnetron, a, described herein.

Zirconium nitride is an electrically conductive material which has very good optical reflectance in the infrared spectrum; however, this material is very absorbing in the visible portion of the spectrum and cannot be used on devices requiring high transparency. Silicon nitride, on the other hand, is 20 very transparent in the near UV through the near IR spectrum (350 nm, 2.0 microns). It was discovered that mixing zirconium nitride with the silicon nitride creates a composite film that has a high index of refraction (22.10) and excellent transparency in the visible spectrum. The film also demonstrates good chemical and mechanical durability. Furthermore, by employing ccsputtering with dual cathode targets, the index of refraction of the film can be adjusted by varying the amdunt of power to each cathode and/or the 30 gases used in the process. The index of refraction of the film so fabricated ranges from approximately 2.00 to 2.45.

Besides SiZrN, composite films comprising titanium nitride and silicon nitride (collectively referred to herein as "SiTiN") or comprising hafnium nitride and silicon nitride (collectively referred to herein as "SiHfN") can also be used. SiTiN and SiHfN composite films are also prepared by cosputtering from dual or single targets. Finally, a composite film comprising a mixture of silicon nitride, zirconium nitride, titanium nitride, and/or hafnium nitride can be used as the first dielectric layer. As will be described further below, the refractive index of the composite films will vary depending on the relative amounts of the different nitrides that comprise each film.

It has been found that when silicon nitride is used as the first dielectric layer, the visible light transmission of the inventive filter is slightly less than the transmission when titanium oxide or a composite film is used.

The thickness of the first dielectric layer ranges from approximately 200 to 500 A, and more preferably from approximately 300 to 350 A.

As shown in Fig. la, the inventive filter next comprises first metal precoat 10 that is deposited over the first dielectric layer. Precoat layer 10 is preferably maintained as thin as possible so that it will have very little, if any, adverse effect upon the optical characteristics of the filter or the subsequent metal layer. Precoat layers with thicknesses ranging .**.from approximately 5 to 20 A have been satisfactory; more preferably, the thickness is between approximately\ 3 to 16 A. This thin precoat layer can be formed from any number of metals. It has been found that nickel- 30 chromium alloy comprising approximately 1 to 80 percent nickel and approximately 1 to 20 percent chromium can be used as a precoat; more preferably, the alloy content is approximately 80 percent nickel and 20 percent chromium.

Other metals and alloys thereof that can be used as a Sprecoat include nickel, chromium, rhodium, platinum, f K tungsten, molybdenum, and tantalum. See Hart, U.S.

Patent 4,462,883, issued July 31, 1984. The precoat layer apparently acts as a glue or nucleation layer and as a stress reducing layer. It is believed that while the precoat layer is thin enough not to adversely affect the optical properties of the filter, it causes the metal film 12 to behave as if it were a homogeneous metal slab.

Next, a partially reflective metal layer 12 is deposited onto the first precoat layer. The metal layer reflects infrared-radiation, yet allows for sufficient visible light transmission. The metal layer can be formed from a number of materials, with silver being particularly satisfactory.

Other metals which also can be utilized include gold, copper and platinum. The thickness of the metal layer ranges from approximately 40 to 150 A, and more preferably, from 15 approximately 90 to 110 A.

In this preferred embodiment, a second metal precoat layer 14 is then deposited onto the metal layer which is followed by the final dielectric layer 16. This second metal precoat layer can be formed from any of the materials and in 20 the thickness range described above for precoat layer The second dielectric layer can be made of silicon nitride that is formed by reactive sputtering a cylindrical magnetron, This layer has a thickness from approximately 350 to 500 A, and more preferably from approximately 450 to 475 A. Any of the above referenced composite films can also be used although the relative proportion of silicon nitride in each film is adjusted so that the refractive index ranges preferably from approximately 2.04 to 2.10. When a composite film is used, its thickness should be from approximately 300 to 500 A, preferably 350 to 375 A. However, whether silicon nitride or a composite substance is used as the second dielectric layer, the layer most preferably exhibits low intrinsic stress as described further below. A suitable composite film is SiZrN comprising approximately 80-83% by weight silicon nitride and the balance zirconium nitride.

This particular film has a refractive index of approximately 1.85 to 2.2. A preferred SiZrN composite film has a O 941129,p:\opcr\phhl,9890-92333,7 s~p't-I

I,

I,,

rE -8refractive index of about 2.08. In accordance with the invention, one or each of the dielectric layers comprises one of the above described composite films. As will be described below, the described filters can offer excellent mechanical and corrosion resistance.

The precoat and metal layers were deposited with a D.C.

planar magnetron. Other techniques including E-beam evaporation could have also been employed. The dielectric layers of the inventive filter were prepared by DC-reactive sputtering with a rotating cylindrical magnetron. The magnetron reactive sputtering technique is particularly useful for depositing dielectric films. While there are other techniques for depositing the dielectric layers such as thermal oxidation and LPCVD (low pressure chemical vapor 15 deposition), these methods suffer from, among other things, 0:0, slow deposition rates. Moreover, RF planar magnetron sputtering for depositing dielectric material is impractical for large-scale industrial applications because of the 2 enormous power requirements and RF radiation hazards. A description of a cylindrical magnetron suitable for depositing substrates with the dielectric materials is found in Wolfe et al., U.S. Patent 5,047,131, issued September 1991, incorporated herein by reference. To provide additional protection to the inventive filter, a plastic laminate can be applied to the filter of Fig. la. See Young et al., U.S. Patent 4,965,121, issued October 23, 1990 incorporated herein by reference.

C

In fabricating the described filter, it was found that by reducing the intrinsic stress of the second dielectric layer 16, an extremely hard and chemically resistant thin film coating is produced.

*j 9411129,p:\oper\phh,2989-92.333,8 Stress is an important variable that is inherent in each layer of a thin film stack. There are generally two stress states: compressive, where the film is trying to expand on the substrate and, tensile, where the .film is .trying to contract. In magnetron systems, the pressure of .the vacuum depositing chamber is an important factor which influences stress. It is believed that at sufficiently low pressures, sputtered atoms and reflected neutral gas atoms impinge on the film at nearly normal incidence with high energy because at lower pressures there are fewer collisions within the plasma (larger mean free path). This mechanism, as reported by Hoffman and Thorton in Thin Solid Films, 355 (1977), is known as "atomic peening", and is believed to cause compression in films.

At higher working pressures, the sputtered atoms collide with atoms in the plasma more frequently.

Sputtered material reaches the substrate at oblique incidence and with lower energies. The decrease in S 20 kinetic energy of the incident atoms makes the peening

S

t mechanism inoperative. The decrease in the flux of atoms arriving at normal incidence results in "shadowing" voids remaining from the nucleation stage of film growth are not filled because nucleation sites 25 shadow the obliquely arriving atoms. Shadowing and 'competing cone growth" can lead to isolated columnar grain structures and an extensive void network. Messier and Yehoda, J. Appl. Phys., 58, 3739 (1985).

Whatever the cause of internal stress in 30 sputtered films, there is, for a given set of system parameters magnetron geometry, deposition rate, film thickness, gas pressure), an abrupt transition from compression to tension at a critical pressure which depends on the atomic mass of the material. (Hoffman and Thorton, Thin Solid Films, 45, 387 (1977); Hoffman and Thorton, J. Vac. Sci. Technol., 20, 355 (1982); Hoffman and Thorton, J. Vac. Sci. Technol., 17, 380 (1980).) Above this critical pressure, tensile stresses gradually decrease to zero. The relaxation of stress beyond some maximum tensile stress point was reported for chromium sputtered in argon and molybdenum sputtered in- xenon. Shih- et al. "Properties- of Cr-N- Films Produced by Reactive Sputtering", J. Vac. Sci. Technol.

A4 May/June 1986, 564-567.

In depositing silicon nitride as-the second dielectric layer with a rotatable cylindrical magnetron, it was found that the intrinsic stress of the silicon nitride layer can be reduced by orienting the magnetic assembly of the cathode at an acute angle. As shojn in Fig. 2, which is a cross-sectional view of cathode S. 15 and substrate 21, the magnetic assembly 18 has a "W" configuration with three elongated magnetics 24, 26, and 28. The permanent magnetics used formed an unbalanced system which is typical for rotatable cylindrical magnetrons. As is apparent, the assembly is oriented at ?0 an acute angle a of approximately 450 so as to direct sputtered material towards the substrata 29 as it enters the deposition chamber. Angle a can range from approximately 300 to 860. Silicon nitride layers so deposited have approximately one-fourth the intrinsic 25 stress of silicon nitride layers produced when the assembly is at a normal angle relative to the substrate.

Experimental Results A low-emissivity interference filter having the structure as shown in Fig. la comprising a glass substrate, a titanium oxide first dielectric layer, nickel-chromium alloy precoat layers, a silver metal layer, and a silicon nitride second dielectric layer was fabricated in an in-line magnetron system manufactured by Airco Coating Technology, a division of Assignee. It is known that Tio 2 is the predominant form of titanium oxide created in the sputtering process. However, it is believed that other forms are produced as well. Thus, unless otherwise stated, TiO 2 will represent all forms of titanium oxide produced. The system comprises 43five magnetrons arranged in series, with each magnetron depositing one of the five layers of the filter. The second, third, and fourth are planar magnetrons for depositing the first precoat, metal, and second precoat layers respectively. The planar magnetrons, each comprising ef a model HRC-3000 unit, were manufactured by Airco Coating Technology. The first and fifth magnetrons are cylindrical magnetrons to deposit the dielectric layers. The cylindrical magnetrons, each comprised of a C-Mag M model 3000 cathode, also manufactured by Airco Coating Technology.

S. The target(s) for each of the cylindrical magnetrons was conditioned using an inert gas, thereafter the process gas was added until the desired partial pressure was reached. The process was operated at that point until the process was stabilized. The substrate was then introduced to the coat zone of the first cylindrical magnetron and the film was applied.

The substrate used was soda lime glass.

For depositing a first dielectric layer 25 comprising of titanium oxide, a C-MAG M rotatable magnetron employing a titanium target was used.

Alternatively, a planar magnetron can be employed.

Argon was the inert gas and oxygen was the reactant gas.

When depositing silicon nitride in the cylindrical magnetron, argon was used as an inert gas and nitrogen was used as the reactant gas. The partial pressure of the gas was determined by the transition from the nitride mode to the'metallic mode. Experiments were run as close to that transition as practicable. The pressure and flow rate of the sputtering gases were ccntrolled by conventional devices.

I I 12 Because the electrical conductivity of pure silicon is so low that it is unsuitable for sputtering with direct current, the silicon target was impregnated or doped with a small amount of aluminum in the range of from The target was prepared by plasma spray.

The"sputtering source was connected to an appropriate direct current power source having provision for automatically maintaining the voltage, current or power, as desired. The magnet assembly of the single cathode was oriented at an angle of approximately 450 from normal.

With nitrogen as the sputtering gas, the i coating contained a mixture of aluminum and silicon nitrides. All of these components are relatively hard and form an amorphous film that acts as a strong barrier. However, the amount of aluminum in the film .did not interfere with formation of the desired silicon based compound films. In the course of the experiments, films were sent out for independent RBS (Rutherford Back-Scattering) sampling to determine the composition of the compound. The silicon nitride measured 42% Si/57% N, which is very close to the theoretical 3:4 ratio for nitride (Si 3

N

4 Table 1 sets forth the process data for deposition of an inventive filter.

25 TABLE 1 FLow- Flow- Flow- Sub- Thick- rate rate rate Poten- Pres- strate ness (SCCH) (SCCH) (SCCM) tial Power sure No. Speed Layer M Ar -H2- v L (kW) Passes (in/min) Ti02 327 71 0 131 -371 40 1.5 8 47 NiCr 12 170 0 0 -444 1 3.0 1 154 Ag 100 69 0 0 -552 10 1.5 1 154 NiCr 12 170 0 0 -444 1 3.0 1 154 Si 3 4 461 12 60 0 -387 15(x2) 5.0 2 31 13 The above filter had the following optical and electrical characteristics: 82.4 Transmittance (integrated D65 source) 6.1 Reflectance of the film covered side 11.5 Absorbance 10.5 n/o Electrical sheet resistance .0.09: Emissivity The durability of the inventive filter of Table 1 was tested. The procedures of the chemical and mechanical tests that were performed are described in Table 2. The inventive filter passed all the tests.

Curve 1 in Fig. lb illustrates the reflectance of the interferance filter produced under the parameters set forth in Table 1 as from the film side. Curve 3 is 15 the reflectance of the uncoated substrate side and curve is the transmittance. The measurements were performed with a scanning spectrophotometer.

TABLE 2 Test Conditions and Scoring Procedures 9* 9 99* oo e o* 9 9 9999 99* 9 99 *9 .9 .9.9 9.r 99 *9 .9 9999*9 9 9 1. Humidity Test 2. Salt Fog Test 3. UV Exposure Test 4. Ammonium Test Exposures in a humidity cabinet for: 24 hrs. at 90 0 C and 98% RH and 96 hrs. at 60 0 C and 98% RH.

20% Salt Fog, 95-98 0 F for 72 hrs.

Exposure for 24 hrs. with cycles of 4 hrs. condensation until failure or 120 hrs.

Samples are placed upright in closed container of 50% ammonium hydroxide solution at room temperature for 5 hrs.

A 1% salt solution is applied to a filter paper dot placed on the film with the sample placed in a constant humidity environment for 24 hrs.

Salt Dot Test S1 14 Evaluations of the above tests are based on both microscopic evaluation and emissivity measurements. The details of the evaluations are: A. Samples are scored for evidence of microscopic corrosion as seen under 200x magnification on a scale of 1 to 10, where 10 is unaffected and 1 is completely corroded.

Measure the change in emissivity due to corrosion. The scoring is based on: Emissivity Score 10 (Emiss. before/Emiss. after) C. Recorded scores are an average of 1 and 2 Taber Abrasion Samples are subjected to a total of 50 revolutions on the Taber abrader, using the standard 500 15 gram weight and CS-10F wheels.

Evaluation is based on the average number of scratches seen under 50x magnification in 4 inch 2 areas. Using Sthe equation below gives a score of 0 for more than scratches in a 1" square area and 10 for none: Taber Score 10 scratches) x (0.18)] As stated above, in other embodiments of the inventive filter, one or both of the dielectric layers can comprise of composite films of either SiZrN, SiTiN, SiHfN, or mixtures thereof. For each composite, the relative amount of silicon nitride ranges from approximately 60-95% by weight depending on whether the composite is used as the first or second dielectric layer. The index of refraction of the composite film correspondingly ranges from approximately 2.4 silicon nitride) to approximately 2.05 (95% silicon nitride).

One method of depositing composite films is cosputtering of a cylindrical magnetron employing dual targets with one target being made of silicon and the 0 4 1 other target being made of either zirconium, titanium, hafnium, or mixtures thereof. When cosputtering with dual cathodes with nitrogen as the reactant gas, the angle of the magnetic assembly of each target can be adjusted to get homogeneous composition distribution.

See i Pp i nI I 4-Obrfrs' f- M)cd %r-h Iq 1 1 99-1 -f common assignee, and Belkind et al., "Reactive Co-Sputtering of Oxides and Nitrides using a C-MAG" Rotabable Cylindrical Cathode," Surface and Coating Technology, 49 (1991), 155-160.

Another method of depositing composite films is to have one or more alloy targets, each coated with silicon and either zirconium, titanium, hafnium, or a mixture thereof. A process for fabricating cylindrical 15 alloy targets involves doping silicon and another metal (or other metals) to form a conductive silicide. For instance, doping silicon and zirconium results in forming ZrSi;, a conductive silicide that possesses a bulk resistivity of approximately 160 micro ohm cm.

This material is conductive enough to be sputtered by a magnetron. The silicide can be synthesized by heating zirconium and silicon together (hot press technique) to a sufficient temperature to form ZnSi 2 Thereafter, the silicide is grounded to a powder and sprayed onto a 25 stainless steel backing tube to form a homogeneous coating.

ZnSiN composite films were formed by cosputtering a C-MAG rotatable magnetron system manufactured by Airco Coating Technology. The system employed dual cathode targets wherein the angle the magnetic assembly of each target was set at approximately 450 relative to normal so as to focus the ZrN and Si 3

N

4 molecules onto the glass substrates. It is believed that ZrN is the predominant form of zirconium nitride created in the sputtering process, although other forms may be produced as well. Thus, unless I 1 16 otherwise- stated, ZrN will represent all forms of zirconium nitride sputtered.

With dual targets, the relative amounts of reactively sputtered material deposited from each target can be regulated, in.part, by-adjusting the power to each-target. Employing this.technique, three different ZrSiN composite films were deposited., The:first film comprised of approximately 60% Si 3

N

4 and 40% ZrN (60/40), the second comprised of approximately 72% Si 3

N

4 and 28% ZrN, and the third comprised of approximately 83% Si 3

N

4 and 17% ZrN (83/17).

Curves 30 and 32 in Fig. 3 illustrate the percentage transmission in the visible light region for films one (60/40) and three (83/17), respectively; 15 curves 40 and 42 in Fig. 4 illustrate the percentage reflection in the visible light region for films one (60/40) and three (83/17), respectively; and curves and 52 in Fig. 5 illustrate the percentage absorption for films one (60/50) and three (83/17), respectively.

Table-3 sets forth the refractive index (n) and extinction coefficient values versus wavelength for the first composite film (60% SigN4, 40% ZrN), and Table 4 sets forth the optical values versus wavelength for the second composite film (72% Si 3

N

4 28% 25 ZrN). (The optical values were measured by an ellipsometer.) TABLE 3 .t.

9*

S.

*US.

S. S *9 4 S S S S *5 *5

S

380' 400.

.420~ 440- -460.

480 500 520 540 560 8 0 600C 620 640 660 680 700 720 740 760 780 800 820 840 6860 880 900 920 940 960 980 1000 2000 -n 2.600 2.566 57 2.542 2.521 2.500 2.472 2.463 2.449 2.436 2.424 2.412 2.404 '1 396 389 2.382 2 .376c 2.371 2.366 2.361 2.*356 2.353 2.349 2.*347 2.344 2.341 2.338 2.337 2.335 2.332 2.332 2.329 2.300 -k 0.0500 0. 0500 0. 0400 0.0350 0. 0300 0. 0250 0. 0200 0. 0150 0. 0150 0. 0150 0.0100 0.*0110 0.0090 0. 0080 0. 0070 0. 0060 0.0060 0. 0060 0.0060 0.*0050 0.0040 0.0030 0. 0030 0. 0001 0. 0000 0. 0000 0. 0000 0.0000 0.0000 0.0000 0. 0000 0.0000 0. 0000 b 0 18 TABLE 4 X. n k 300 2.4972 0.1768 350 2.3298 0.0718 400 2.2752 0.0400 450 2.2298 0.0156 500 2.2122 0.0071 550 2.1957 0.0001 600 2.1886 0.0028 650 2.1813 0.0051 700 2.1779 0.0060 800 -2.1724 0.0070 1000 2.1673 0.0070 2000 2.1500 0.0070 *0*S e 15 As is apparent, refractive index in the visible region was higher for the first composite film which has less Si 3

N

4 Although the invention has been described with respect to its preferred embodiments, it will be 20 understood that the invention is to be protected within the full scope of the appended claims.

*e *ooo

Claims

1. A thin film interference filter comprising: a transparent substrate; a first dielectric layer; a first metal precoat layer; a partially reflective metal layer; a second metal precoat layer; and a second dielectric layer in which one of the dielectric layers is a composite comprising a mixture of silicon nitride and one or more of zirconium nitride, titanium nitride, and hafnium nitride.

2. A thin film interference filter according to Claim 1 in 15 which said one dielectric layer is a composite comprising silicon nitride and zirconium nitride.

3. A thin film interference filter according to Claim 1 or Claim 2 in which said one dielectric layer comprises about 20 to 95% by weight of silicon nitride.

4. A thin film interference filter according to any preceding claim in which the other dielectric layer comprises siltcon nitride.

5. A thin film interference filter according to claim 4 in which the other dielectric layer is also composite and comprises a mixture of silicon nitride and one or more of zirconium nitride, titanium nitride, and hafnium nitride.

6. A thin film interference filter according to Claim 5 in which the other dielectric layer comprises silicon nitride and zirconium nitride.

7. A thin film interference filter according to Claim 5 or Claim 6 in which the other dielectric layer comprises about to 95% by weight of silicon nitride. 941129,p:\opcr\ph.29890'92.333,19

8. A thin film interference filter according to any preceding qlaim in which the first dielectric layer has a thickness of about 200 to 500 A.

9. A thin film interference filter according to Claim 8 in which the first dielectric layer has a thickness of about 300 to 350 A. A thin film interference filter according to any preceding claim in which the second dielectric layer has a thickness of about 300 to 500 A.

11. A thin film interference filter according to Claim 10 in which the second dielectric layer comprises silicon nitride 15 having a thickness of about 350 to 500 A, preferably of about 450 to 475 A. 0 ea *e

12. A thin film interference filter according to Claim 10 in which the second dielectric layer has a thickness of about 350 to 375 A.

13. A thin film interference filter according to any preceding claim in which one or both metal precoat layer is a formed from a metal selected from one or more of nickel, 25 chromium, tungsten, and platinum or alloys thereof and in t which the partially reflective metal layer is formed from one or more of silver, gold, copper, and platinum or alloys thereof.

14. A thin film interference filter according to Claim 13 in which one or both precoat layer is a metal film wherein the metal elements comprise about 80 to 95 weight nickel and to 20 weight chromium.

15. A method for the production of a thin film interference filter on a transparent substrate, with the filter having a substantially neutral visible reflected colour, comprising 94i129,p:\oper\phh,29890Z333,20 -21- the steps, in sequence, of: reactively sputtering a first substantially transparent dielectric layer onto said substrate; depositing a first metal precoat layer; depositing a partially reflective metal layer; depositing a second metal precoat layer; and reactively sputtering onto said second metal precoat layer a second substantially transparent dielectric layer comprising a composite of silicon nitride and one or more of zirconium nitride, titanium nitride, and hafnium nitride.

16. A method of producing an interference filter according to Claim 12 in which the step of reactively sputtering the 15 second dielectric layer comprises the steps of: providing a cylindrical magnetron having a silicon coated rotatable target and having magnetic means disposed at an angle of approximately 300 to 80* from normal relative to the substrate; and moving the substrate towards the rotatable target so that dielectric material reactively sputtered from the target is focused onto the substrate as it approaches the target.

17. A thin film interference filter according to Claim 1 and substantially as hereinbefore described with reference to the drawings and/or Examples.

18. A method for the production of a thin film interference filter according to Claim 1 and substantially as hereinbefore described with reference to the drawings and/or Examples. DATED this 29th day of November, 1994. THE BOC GROUP, INC. By its Patent Attorneys DAVIES COLLISON CAVE S .941129,p:\oper\phh,29890-92.333,21 DURABLE LOW-EMISSIVITY SOLAR CONTROL THIN FILM COATING Abstract of the Disclosure An infrared reflecting interference filter capable of-transmitting a desired proportion of visible radiation while reflecting a large portion of incident solar radiation is provided. The filter consists of a transparent substrate coated first with a dielectric layer, next a partially metal reflectance layer, and finally an outer protective dielectric layer. In 10 addition, between each metal-dielectric interface is S. deposited a nucleation or glue layer that facilitates adhesions and improves chemical and mechanical resistance. The interference filters are durable and can be modified to provide a full range of optical and 15 electrical characteristics. The dielectric layer can comprise of composite films consisting of silicon .i nitride in combination with zirconium nitride, titanium nitride, and/or hafnium nitride.