JPH07111482B2 - Multi-layer antireflection film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multi-layered antireflection film formed on a transparent substrate in order to reduce the reflection of light on the surface of the transparent substrate. Thus, it is most suitable for application to a face surface of a cathode ray tube used for a television receiver or the like, and an antireflection plate arranged in front of this face surface.

[Outline of Invention]

According to the present invention, a first high-refractive index film, a first low-refractive index film, a second high-refractive index film and a second low-refractive index film are sequentially formed on a transparent substrate in a direction away from the transparent substrate. In the laminated multi-layer antireflection film, at least one of the first and second high refractive index films is provided with a high refractive index first film-like body formed by reactive sputtering. The second film-shaped body having a higher refractive index than the first film-shaped body is laminated, and the first and second film-shaped bodies and the first and second low refractive indexes are formed. By setting the refractive index of the film within a predetermined numerical range, high throughput and high uniformity,
Further, it is possible to provide a large-area multilayer antireflection film having excellent spectral reflectance characteristics at low cost.

[Conventional technology]

In general, in optical equipment such as cameras and binoculars, in order to eliminate phenomena such as flare and ghosts and improve image contrast and sharpness, the surface of glass substrates such as lenses is made of a transparent material called a coating material. An antireflection film is deposited. As is well known, the antireflection film reduces the reflection of light on the surface of a transparent substrate such as a glass substrate and increases the transmittance.

Such an antireflection film is formed not only on a small area such as the lens as described above, but also on a large area.
For example, the antireflection film is formed on the face surface of a cathode ray tube used in a television receiver or the like, or on the surface of an explosion-proof glass plate arranged in front of the face surface.

Antireflection films that have been commonly used in the past include single-layer, double-layer and triple-layer structures. Among them, the single-layer antireflection film having the simplest structure has an antireflection effect only for a single wavelength. However, since the glass substrate that is normally used has a refractive index of ng = 1.52, it is a transparent material that makes the reflectance zero, that is, the refractive index that is the amplitude condition of the reflected light. Since there is no low refractive index film satisfying the above conditions, residual reflection occurs.

The two-layer antireflection film has a structure in which a high refractive index film is interposed between a glass substrate and a low refractive index film. According to this two-layer antireflection film, the apparent refractive index of the glass substrate can be increased by the interposition of the high refractive index film, so that the selection range of the material of the low refractive index film is widened and the above-mentioned residual reflection is eliminated. However, in the case of this two-layer antireflection film, the antireflection effect is limited to a single wavelength and a narrow wavelength region in the vicinity thereof.

The three-layer antireflection film is effective in expanding the antireflection wavelength region. That is, in the case of a two-layer structure, a film having an intermediate refractive index is interposed between the high-refractive index film and the glass substrate, so that the reflectance is zero in two wavelengths and the intermediate wavelength region. It can be extremely small.
Further, in the case of such a three-layer structure, in order to obtain a desired antireflection effect, the refractive index and the film thickness of each transparent material constituting each film can be set within a wide range to some extent, and therefore, there is a degree of freedom in design. Can be improved.

Here, in the case of a multilayer structure of two layers or more,
As for the setting of the refractive index and film thickness of each transparent material, a systematic method has not been established, so in general, the reflected light is calculated based on a vector method that handles reflected light in vector or a complicated matrix method. It is carried out by trial and error to satisfy the phase condition and the amplitude condition as desired.

By the way, the antireflection effect in the visible light wavelength region (wavelength: 400 to 700 μm) cannot be sufficiently obtained with a three-layer structure. In order to meet this requirement, a 4-layer structure has been developed in which the medium-refractive index film of 3-layer structure is further replaced by a high-refractive index film and a low-refractive index film (in order from the glass substrate side). Also in this case, the setting of the refractive index and the film thickness of each transparent material is, of course, carried out by trial and error based on the above-mentioned vector method or the like, but in order to obtain the desired spectral reflectance characteristic, it is generally the glass substrate side. The high and low refractive index films are thin,
Further, the high refractive index film and the low refractive index film formed thereon are made thicker.

With such a four-layer structure, the number of boundary surfaces of the film increases and light interference is enhanced, so that a substantially good antireflection effect can be obtained over the entire visible light range. Further, according to the four-layer antireflection film, the degree of freedom in design can be further increased.

Next, the structures and spectral reflectance characteristics of the conventional four-layer antireflection film and the four-layer antireflection film in the reference example of the present invention will be described with reference to FIGS.

First, FIG. 3 shows a conventional four-layer antireflection film, in which MgF ₂ (magnesium fluoride; n = 1.38), which is a typical low refractive index film material, is used. Note that Mg
F ₂ has a problem that the glass substrate on which the antireflection film is formed is also limited to a small area because its formation method is generally limited to the vacuum vapor deposition method due to its characteristics. There is a point.

In the figure, 11 is a glass substrate (n = 1.52), 12 is a Z with a film thickness of 140 Å
The first high-refractive index film made of rO ₂ (zirconium oxide; n = 2.13), 13 is the first low-refractive index film made of MgF ₂ having a film thickness of 310 Å, 14 is the _second film made of ZrO ₂ having a film thickness of 1320 Å High refractive index film,
Reference numeral 15 is a second low refractive index film made of MgF ₂ having a film thickness of 940Å.

FIG. 5a shows the spectral reflectance characteristic of the conventional example shown in FIG. 3 configured as described above. As is clear from the figure, in this conventional example, the MIL indicated by the shaded area
It fully meets the standards and has excellent characteristics over almost the entire wavelength range of visible light.

Here, as the material of the first and second high refractive index films 12 and 14, in addition to ZrO ₂ described above, Ta ₂ O ₅ (tantalum oxide; n = 2.1) is used.
5), Pr ₆ O ₁₁ (praseodymium oxide; n = 2.20), TiO ₂ (titanium oxide; n = 2.35), or other transparent material suitable for vacuum vapor deposition or reactive DC sputtering can be used.

Next, FIG. 4 shows a four-layer antireflection film in a reference example of the present invention. In this case, a large-area substrate is used as a glass substrate, and a high refractive index film and a low refractive index film are respectively reacted. DC direct current sputtering is used.

As a typical material of the low refractive index film suitable for reactive DC sputtering, SiO ₂ (silicon oxide; n =
1.455), but the refractive index of this SiO ₂ is n = 1.455.
Since the low refractive index film is relatively large, it is necessary to use n = 2.3 to 2.5 as the material of the high refractive index film for convenience of combination. Therefore, in this reference example, a four-layer antireflection film was formed using TiO ₂ (titanium oxide; n = 2.35), which is a transparent material having a refractive index in the above range and suitable for reactive DC sputtering. There is.

In FIG. 4, 11 is a glass substrate, 12 and 13 are film thickness 110Å
First high-refractive index film composed of TiO ₂ and SiO ₂ having a film thickness of 360 Å
Is a first low refractive index film composed of
Second high-refractive index film made of 20Å TiO ₂ and S with 900Å film thickness
It is a second low refractive index film made of iO ₂ .

In the case of the large-area reference example shown in FIG. 4, the spectral reflectance characteristic is excellent as compared with the above-described conventional example shown in FIG. Even if MI
Satisfy L standard sufficiently.

Here, as the first and second low refractive index films 13 and 15, in addition to the above-mentioned SiO ₂ simple substance, Si suitable for reactive DC sputtering is used.
A transparent material containing O ₂ as a main component can be used. Further, as the first and second high refractive index films 12 and 14, in addition to the above TiO ₂ simple substance, TiO ₂ suitable for the same sputtering as a main component can be used. And a transparent material can be used as appropriate.

[Problems to be solved by the invention]

However, in the above-mentioned conventional example shown in FIG. 3, since MgF ₂ is used for the low refractive index film, it is generally necessary to rely on the vacuum deposition method to form this low refractive index film. Therefore, there is a problem in that the area of the antireflection film cannot be increased and the applicable range is limited to a small area such as a lens.

Further, in the case of the above-mentioned reference example shown in FIG. 4, since the reactive direct current sputtering method is used, a large area can be achieved,
Although it can be applied to a glass substrate having a large size (for example, an antireflection plate arranged in front of a cathode ray tube), since MgF ₂ is not used due to technical restrictions at the time of manufacturing, a problem caused by this occurs.

That is, since the refractive index of SiO ₂ is n = 1.455 and is relatively large for a low refractive index film, it is necessary to use TiO ₂ having a relatively high refractive index as a material for the high refractive index film, but TiO ₂ is reactive. Since the DC sputtering rate is small, the second high refractive index film 14
There is a problem in that the productivity becomes extremely low due to the need to form the film particularly thick, which increases the cost.

In addition to TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , P
It is also possible to use r ₆ O ₁₁ etc., but these ZrO ₂ , Ta ₂
Since O ₅ and Pr ₆ O ₁₁ have a refractive index of 2.2 or less, in the four-layer antireflection film shown in FIG. 4, another example of the present invention using Ta ₂ O ₅ as the high refractive index films 12 and 14 is used. In the case of the reference example, the spectral reflectance characteristic is as shown in FIG. In this case, as is clear from the figure, there is a wavelength region (C in the drawing) that has almost no margin or cannot meet the MIL standard, and the spectral reflectance characteristic deteriorates.

In the case of the above-mentioned other reference example whose spectral reflectance characteristics are shown in FIG. 6, the film thickness of Ta ₂ O ₅ used as the first and second high refractive index films 12 and 14 is 140Å, And 1130Å and used as the first and second low refractive index films 13 and 15
The film thicknesses of O ₂ are 270 Å and 850 Å, respectively.

The present invention has been made in view of the above-mentioned problems, and can be applied to a large-area transparent substrate from a practical point of view,
An object of the present invention is to provide a multilayer antireflection film capable of forming a high refractive index film and a low refractive index film uniformly and efficiently.

[Means for solving problems]

The present invention relates to an antireflection film formed on a transparent substrate such as a glass substrate or a synthetic resin substrate to reduce the reflection of light on the surface thereof. The low refractive index film of 1, the second high refractive index film and the second low refractive index film are multilayered, and these films are formed on the transparent substrate in the order described above in the direction away from the transparent substrate. In the sequentially formed multilayer antireflection film, at least one of the first and second high refractive index films has a high refractive index first film-like body formed by reactive sputtering, The second film-shaped body having a refractive index higher than that of the first film-shaped body is laminated, and the refractive index of the first film-shaped body is 1.9 to 2.2. The refractive index of the film body is 2.2 to 2.5, and the refractive index of the first low refractive index film is
1.44 to 1.65, and the refractive index of the second low refractive index film is 1.
It relates to a multilayer antireflection film having a thickness of 44 to 1.50.

In the present invention, the refractive index of each of the first and second low refractive index films may be 1.44 to 1.50, and
The first low refractive index film may have a refractive index of 1.50 to 1.65, and the second low refractive index film may have a refractive index of 1.44 to 1.50.

According to the present invention configured as described above, the first of the first and second film-like bodies forming at least one high refractive index film, which has a relatively low refractive index of 1.9 to 2.2, Since the film-like body of is formed by using reactive sputtering, it is possible to increase the sputtering rate. Therefore, a large-area multi-layer antireflection film can be formed with high throughput and high uniformity, and at low cost. Can be provided at. In addition to the first film-like body formed by the reactive sputtering, a second film-like body having a higher refractive index of 2.2 to 2.5 is provided in the at least one high refractive index film, The refractive indices of the first and second low low refractive index films are respectively
Since it is sufficiently low at 1.44 to 1.65 and 1.44 to 1.50, excellent spectral reflectance characteristics can be obtained.

In the present invention, one of the first and second high-refractive index films is configured to be sufficiently thicker than the other, and only the one high-refractive index film is formed from the first and second film-like bodies. Consists of
Further, the first film-shaped body is configured to be sufficiently thicker than the second film-shaped body, and is located immediately outside the one high refractive index film of the first and second low refractive index films. It is preferable that the low-refractive-index film is sufficiently thicker than the other low-refractive-index film. And by configuring like this,
Throughput can be further improved, and more excellent spectral reflectance characteristics can be obtained.

In addition, as the reactive sputtering for forming the first film-shaped body, when the first film-shaped body is made of Ta ₂ O ₅ alone or a substance containing this as a main component, the sputtering rate is It is preferable to use reactive DC sputtering which can increase the temperature.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2.

In FIG. 1, 11 is a large-area glass substrate (n = 1.52)
Transparent substrate, 12 and 13 are made of TiO ₂ (n = 2.3
The first high refractive index film composed of 5) and SiO ₂ (n of 395 Å)
= 1.455), and these films 12 and 13 function to change the apparent refractive index of the glass substrate 11. 14a is Ta ₂ O ₅ (n = 2.1 with a film thickness of 1015Å).
5) is a first film-like body, and 14b is a second film-like body made of TiO ₂ having a film thickness of 180 Å. The first and second film-like bodies 14a and 14b provide a second high refractive index. A rate film is constructed. Further, 15 is a second low refractive index film made of 960Å SiO ₂ .

In this five-layer antireflection film, the films 12, 13, 14a, 14
The transparent material constituting b and 15 is selected so as to satisfy the phase condition and amplitude condition of the reflected light as desired in order to make the reflectance zero or extremely small in the visible light wavelength region, and the film thickness is Each is set.

In addition, in the production of the above-mentioned five-layer antireflection film, the reactive magnetron sputtering method is used, and the reactive direct current is applied under the condition of the pressure of 5 × 10 ⁻³ Torr with the mixed gas of 85% Ar-15% O ₂ as the atmosphere gas. Sputtering is performed.

The first film-shaped body 14a in the second high refractive index film, which is the thickest and requires the longest sputtering time in the SiO ₂ —TiO ₂ —Ta ₂ O ₅ -based five-layer film, is formed from Ta ₂ O ₅ Although made, the time required for a large sputtering rate of the Ta ₂ O ₅ in the sputtering of Ta ₂ O ₅ requires only about 5 minutes. On the other hand, when the entire second high-refractive index film is composed of TiO ₂ (which has a SiO ₂ —TiO ₂ system structure and is the same as the above-mentioned reference example shown in FIG. 4), TiO ₂ is used as described above. Because the sputtering rate of is low,
Even if the film is formed under the same manufacturing conditions as in this embodiment, the time required for sputtering the second high refractive index film TiO ₂ is about 27 minutes.

As described above, according to the present embodiment, the first film body 14a made of Ta ₂ O ₅ having a high sputtering rate is made thick and the second film body 14b made of TiO _{2 having} a low sputtering rate is formed. Since the second high-refractive-index film is made thin, each of the films 12, 13, 14a, 14b, and 15 can be formed by an in-line process in an in-line type sputtering device, and the five-layer antireflection film is formed. In the case of manufacturing, the formation speed of these five films as a whole is compared with the formation speed of the four films 12, 13, 14, 15 of the SiO ₂ —TiO ₂ -based four-layer antireflection film shown in FIG. , Can be increased by almost 5 times or more.

FIG. 2 shows the spectral reflectance characteristics of the SiO ₂ —TiO ₂ —Ta ₂ O ₅ -based five-layer antireflection film of this embodiment described above.
As is clear from the figure, the five-layer antireflection film in this example fully satisfies the MIL standard shown by the shaded region and has excellent characteristics over almost the entire wavelength region of visible light.

In the above embodiment, in order to obtain the spectral reflectance characteristic satisfying the MIL standard, the first high refractive index film 12 made of TiO ₂ is used.
75 ± 10Å, the first low refractive index film 13 made of SiO ₂ is 395 ± 20
Å, the first film body 14a of the second high refractive index film made of Ta ₂ O ₅
Is 1015 ± 10Å, the second film 14b of the second high-refractive-index film made of TiO ₂ is 180 ± 10Å, and the second low-refractive-index film 15 made of SiO ₂ is in the range of 960 ± 20Å. As described above, each film thickness can be expanded, but it goes without saying that the present invention is not necessarily limited to the above range.

In addition, the first film body 1 of the second high refractive index film made of Ta ₂ O ₅
Second film body 14b of the second high refractive index film composed of 4a and TiO ₂
It was possible to obtain substantially the same effect by reversing the above and below, or, as in the case of the above-mentioned embodiment, the second film-shaped body 14b made of TiO ₂ and having a higher refractive index has the second low refractive index. It was found that the film on the side of the index film 15 has more excellent spectral reflectance characteristics.

Further, even if the set of the films 12 and 13 and the set of the films 14a, 14b, and 15 are turned upside down, substantially the same effect can be obtained, but as in the case of the above-described embodiment, the films 12 and 13 are obtained. It was found that the set of the above was closer to the glass substrate 11 side, and the spectral reflectance characteristic was more excellent.

Furthermore, TiO ₂ was used as the first high refractive index film 12,
Other transparent material having a refractive index of 2.2 to 2.5 or Ta ₂ O _5, ZrO,
₂ , In ₂ O ₃ (indium oxide; n = 2.00), SnO ₂ (tin oxide; n = 2.00), Pr ₆ O ₁₁ , Sb ₂ O ₃ (antimony oxide; n = 1.9)
5), Nd ₂ O ₃ (neodymium oxide; n = 1.90) or a mixture thereof can be used as a transparent material having a refractive index of preferably 1.9 to 2.2. Further, the film thickness can be appropriately set depending on the selected material.

Further, as the first film-shaped body 14a of the second high refractive index film,
In addition to the above Ta ₂ O ₅ , ZrO ₂ , In ₂ O ₃ , SnO ₂ , Pr ₆ O ₁₁ , Sb ₂ O ₃ , N
A transparent material having a refractive index of preferably 1.9 to 2.2 and having a higher sputtering rate than the second film-like body 14b of the second high refractive index film is used as a simple substance such as d ₂ O ₃ or a mixture thereof. Can be used. Further, as the second film-shaped body 14b of the second high refractive index film, other transparent materials having a refractive index of preferably 2.2 to 2.5 can be used in addition to the above TiO ₂ . In this case, both the film thicknesses of the first and second film-shaped bodies 14a and 14b can be appropriately set by the selected material, as in the case of the first high refractive index film 12.

Furthermore, as the first low refractive index film 13, in addition to the above-mentioned SiO ₂ , a simple substance of Al ₂ O ₃ (aluminum oxide; n = 1.64), a mixture thereof, or one or both of them is a main component. A transparent material whose refractive index is preferably 1.44 to 1.
A range of 65 can be used. As the second low refractive index film 15, other single SiO _2, a mixture of SiO ₂ and Al ₂ O _3, or a refractive index of preferably transparent material that the SiO ₂ as a main component from 1.44 to 1.50 It is possible to appropriately select and use one within the range.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to provide a large-area multilayer antireflection film having excellent spectral reflectance characteristics with high throughput and high uniformity, and at low cost.
Therefore, it is extremely practical.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a multilayer antireflection film according to an embodiment of the present invention, FIG. 2 is a spectral reflectance characteristic diagram of the multilayer antireflection film shown in FIG. 1, and FIG. FIG. 4 is a partial sectional view showing an antireflection film, FIG. 4 is a partial sectional view showing a multilayer antireflection film in a reference example of the present invention, and FIG. 5 is a conventional example shown in FIG. 3 and a reference example shown in FIG. FIG. 6 is a spectral reflectance characteristic diagram of SiO _{2 and} FIG. 6 is SiO ₂ in another reference example of the present invention.
FIG. 3 is a spectral reflectance characteristic diagram of a —Ta ₂ O ₅ -based multilayer antireflection film. In the reference numerals used in the drawings, 11 ... Glass substrate (transparent substrate) 12 ... First high-refractive index film 13 ... First low-refractive index film 14a ... First film-like body 14b. Second film 15: The second low refractive index film.

Claims (7)

[Claims] 1. An antireflection film formed on a transparent substrate for reducing light reflection on the surface of the transparent substrate, the first high refractive index film, the first low refractive index film, A multi-layered antireflection film that is composed of a second high-refractive index film and a second low-refractive index film in a multilayer structure, and these films are sequentially stacked on the transparent substrate in the order described above in the direction away from the transparent substrate. In the film, at least one of the first and second high refractive index films has a high refractive index first film formed by reactive sputtering, and the first film. The second film-shaped body having a higher refractive index than that of the second film-shaped body is laminated, and the first film-shaped body has a refractive index of 1.9 to 2.2, and the second film-shaped body has a refractive index of 1.9 to 2.2. 2.2 to 2.5, the first low refractive index film has a refractive index of 1.44 to 1.65, and the second low refractive index film has a refractive index of 1. Multi-layer anti-reflection coating that is 44-1.50. 2. The multilayer antireflection according to claim 1, wherein only the second high refractive index film is formed by laminating the first film body and the second film body. film. 3. The refractive index of the first high refractive index film is 1.9 to 2.2.
The multilayer antireflection film according to claim 2, wherein 4. The refractive index of the first high refractive index film is 2.2 to 2.5.
The multilayer antireflection film according to claim 2, wherein 5. A Ta ₂ O ₅ , ZrO ₂ , and I as the first film-like body.
Any one of n ₂ O ₃ , SnO ₂ , Pr ₆ O ₁₁ , Sb ₂ O ₃ , and Nd ₂ O ₃ ,
Alternatively, a mixture of these is used, and TiO ₂ is used as the second film-like body, and the multilayer antireflection film according to claim 1. 6. The first low refractive index film is SiO ₂ , Al ₂ O.
_3. The multilayer antireflection film according to claim 1, wherein any one of the simple substances of ₃ , or a mixture thereof, or a substance containing one or both of them as a main component is used. 7. The second low refractive index film is made of SiO ₂ , a mixture of SiO ₂ and Al ₂ O ₃ , or a substance containing SiO ₂ as a main component. The multilayer antireflection film according to item 1.