JP2639667B2 - Dual wavelength anti-reflection coating - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer antireflection film in two wavelength regions that are relatively separated, for example, visible light and infrared light.

2. Description of the Related Art A conventional antireflection film is an antireflection film only in a single wavelength region. For example, in a three-layer antireflection film in a visible region, reflection in an infrared region increases more than that of a substrate. Therefore, there is no problem in the case where the wavelength region used is a single wavelength region, but when two wavelength regions, for example, a visible region and an infrared region are used by the same optical system, ghosts and flares are generated or the light amount is insufficient. on the other hand,
The above three-layer anti-reflection film is placed in the infrared region (for example, λ ₀ = 3750 nm)
If it is used to prevent reflection, it becomes difficult to prevent reflection in the visible range. _{However, λ 0/3, λ 0} /5, at a wavelength band of ...... has become a antireflective, conventionally such second, third ...
The anti-reflection band of two wavelength ranges was performed using the anti-reflection band of. However, the wavelength range, as described above λ _0/3, λ ₀
/ 5, …….

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the conventional antireflection film for two wavelength bands, and provides an antireflection film capable of performing antireflection for two wavelength bands that are relatively far apart. It is another object of the present invention to provide an antireflection film having a wide antireflection band of a short wavelength out of the two wavelength bands.

The present invention provides a first substrate refractive index adjusting layer having a refractive index n ₁ and a thickness d ₁ with respect to a center wavelength λ ₁ on a substrate S having a refractive index n _sub , a refractive index n ₂ and a thickness d _2. the first anti-reflection layer are sequentially _{stacked, n 1 d 1 ≒ λ 1} /4, n 2 d 2 ≒ λ 1/4 in, In the film configuration of the antireflection film that satisfies the following relational expression, at least one portion between the substrate S and the first substrate refractive index adjustment layer and between the first substrate refractive index adjustment layer and the first antireflection layer has a refractive index of: n _A ,
n _B, with respect to materials of n _C, n an integer multiple of _{A (λ 1/2),} or n
_{B (λ 1/4) -n} C (λ 1/2) either one of _{-n B (λ 1/4)} , or an anti-reflection film arranged non involvement layer with respect to the wavelength lambda ₁ consisting of combinations The non-participating layer and the first
A multilayer film composed of a substrate refractive index adjusting layer and a first antireflection film is formed such that a center wavelength λ ₁ and a center wavelength λ ₂ (2λ
₁ <λ ₂ ), the total optical film thickness is divided into approximately two equal parts, the refractive indices of the first half and the second half are N ₁ and N ₂ , and the film thickness is D ₁ ,
When the _{D 2, N 1 D 1 ≒} λ 2/4, N 2 D 2 ≒ λ 2/4, Satisfying the following relational expression, the center wavelength λ ₁ in the ultraviolet region:
A two-wavelength region anti-reflection film characterized by preventing reflection in two wavelength regions of a central wavelength λ _{2 in} the visible region with respect to a central wavelength λ _{2 in} the visible region or a central wavelength λ _{1 in the} visible region with respect to the visible region. is there.

The basic type of the principles of the described two-layer antireflection film (V coated), when the refractive index of the substrate S and _{n sub, n sub / n 1} (λ 1/4) -n 2 (λ 1/4) /
It is a two-layer structure of air. Then n ₁ The reflectance 0 at a center wavelength lambda ₁ if the.

For example, BK7 (n = 1.52) /1.70 (λ 1 /4)-1.38(λ 1/4) / air (n 0 =
1) (1) that is to perform efficiently prevent reflection at a certain wavelength lambda _1, the optical thickness _{n 1 d 1 = λ 1/} 4, A substrate refractive index adjusting _{layer, n 2 d 2 = λ 1} /4 of the low refractive index material n ₂
Requires an antireflection layer.

Typically, Al as agents _{n 1 2 O 3, n MgF} 2 as a _second material
Is used.

_{n sub /1.68(λ 1 /4)-1.38(λ 1/4} ) / air ...... (2) Al 2 O 3 MgF 2 However, in the two-layer antireflection film (V coated), lambda ₁
In the vicinity, anti-reflection is provided, but at other wavelengths λ ₂ (> λ ₁ ), the reflectance is usually higher than the reflectance of the substrate itself without the anti-reflection film. In the long wavelength region, when λ ₂ ≫λ _1, it is almost the same as the substrate. In other words, the film thickness is thin and negligible in the long wavelength region.

On the other hand, lambda _2, when performing antireflection by V coating, the shorter wavelengths than _{λ 2, λ 2/3,} λ 2/5, λ 2 /
7, ..., anti-reflection, but the band is very narrow.

lambda _1, in order to perform efficiently antireflection a dual wavelength range of lambda _2, without destroying the properties of V coat at lambda _1, and lambda ₂ substrate refractive index adjusting layer so as to be anti-reflective at lambda ₂ it may be provided lambda ₂ antireflective layer. layer not destroying the lambda ₁ characteristic (layer not involved in lambda _1), when lambda ₂ is shorter according to the wavelength of lambda ₂ is thin, long time to thicken.

And the lambda ₁ is not involved in the layer, the refractive index _{n A, n B, n A} (λ 1/2) with respect to substance _{n C, n B (λ 1} /4) -n C (λ 1/2 ) -N
_{B (λ 1/4),} shows and the like. These characteristic matrices M are . Therefore, it can be seen that not involved in characteristics at lambda _1.

The group of such lambda ₁ not involved layer (I), (II),
(I '), (II' When), a combination of V coat lambda ₁ Any film of the configuration of the V coat of at λ _{1. Here, A: Al 2 O 3 (} λ 1/4) layer, M: shows the MgF ₂ (λ _1/4) layer.

In the configuration of (4), in order to further prevent reflection of λ ₂ , the first half is a λ ₂ substrate refractive index adjustment layer, and the second half is λ 2.
_{2 In} order to become an anti-reflection layer, that is, the equivalent refractive index of several layers in the first half is N ₁ , the film thickness (actual thickness) is D ₁ , and those in the second half are
Assuming N ₂ and D ₂ The refractive index, the number of layers, or the combination of (I), (II), (I '), (II'), etc. may be determined so that

In this case, lambda ₁ not involved layer (I), (II), (I '),
(II '), it is possible to broaden than V coat body antireflection band at lambda ₁ by the inclusion of broadband layer of n (λ _1/2).

(Description of Related Art) First, as shown in FIG. 5, the complex amplitude reflectance r (re ^iδ ) at the interface between the glass substrate and air is represented by a horizontal axis X being a real axis and a vertical axis Y being an imaginary axis. Then, the point O ₁ at −0.20 on the real axis X
(R = 0.20, δ = 180 °). When a thin film is deposited on the glass substrate, the value of r changes.
For example, when deposited on ZnS (n ₁ = 2.30), the optical film thickness n ₁ d
₁ is increased, and a circle with a radius of ▼ is drawn around the point O ₂ (r = −0.39) in FIG. 5, and the distance from the point P on the circumference to the origin O is the amplitude at that time, that is, ▼ represents r. This is called Apfel display.

Next, a two-layer antireflection film will be considered. It is known that in order to make the substrate with n _sub = 1.52 to have 0% residual reflection at λ ₀ using the first layer with n = 1.38, n _sub = 1.52 should be equivalently changed to n _sub = 1.9. ing. For this purpose, as shown in FIG. 6, the material of n = 1.7 λ _1/4 is deposited, further n = 1.38
Substance it can be seen that it is sufficient to λ _1/4 deposition. In FIG. 6, points 10 and 12 indicate regions where the reflectivity is R = 1% and 0.5%, and dotted lines 14, 16, and 18 indicate wavelength ratios ν = 1.1 and ν =
1.2 and ν = 1.3.

If a substance with n = 1.7 cannot be obtained, as shown in FIG. 6, a substance with n> 1.7, for example, ZrO ₂ (n = 2.03)
The substance may be replaced with 2.03 (phase film thickness: δ ₁ ) −1.38 (phase film thickness: δ ₂ ) so as to be equivalent to n = 1.7 with a substance satisfying n <1.7, for example, MgF ₂ (n = 1.38). This is called a two-layer equivalent film (or composite film), and is extremely effective for obtaining a film equivalent to a single-layer film having a refractive index of n _H <n <n _{L at} a short wavelength together with a three-layer symmetric equivalent film. Method.
However, in this case, it is necessary technology for controlling the thickness lambda _0/4 or less.

In the two-layer antireflection film described above, the first half of 1.7
_{(Λ 0 /4),2.03(δ 1) -1.38 (} δ 2) of layers,
Can be considered by 1.38 (λ _0/4) layer of the second half portion for the non-reflective, i.e. the substrate refractive index adjusting layer for the equivalently n _sub '= 1.38 ² ≒ 1.9 the refractive index of the substrate .

These two-layer antireflection films (V coats) are single wavelength region antireflection films, and the reflectance monotonically increases at wavelengths other than the center wavelength as shown by dotted lines 14, 16, and 18 in FIG. 6 depending on the wavelength ratio. I do.

Example (1) (1) UV / visible two-wavelength region antireflection film (λ ₁ = 250 nm,
λ ₂ = 633 nm) Here, 1.63 indicates the refractive index of Al ₂ O ₃ , 1.38 indicates the refractive index of MgF ₂ , 1.46 indicates the refractive index of SiO ₂ , and 1.90 indicates the refractive index of Y ₂ O ₃ .

The two-wavelength region antireflection film having this configuration has a sufficient antireflection effect in the ultraviolet region (center wavelength 250 nm) and the visible region (center wavelength 633 nm) which are relatively far apart.

 This will be described below.

This arrangement a more condition _{(5), n sub (=} 1.50) / N 1 (λ 2/4) -N 2 (λ 2/4) / air ...... (6 ') by a very rough approximation simultaneously You only have to be satisfied. This is indicated by 104 in FIG.

Strictly _{speaking, N 1 (λ 2/4} ) layer is the solid line in FIG. 1 100-
To, N ₂ is (λ _2/4) layer, is equivalent to the solid line 100-, total optical thickness for simplicity (λ _1/4) × half 6 (λ _1/4)
× 3, that is, the portion of _{1.46 (λ 1 /4)-1.90(λ 1/2} ) N 1
Considered _{(λ 2/4), 1.46} (λ 1 /4)-1.63(λ 1 /4)-1.3
Consider the portion of the _{8 (λ 1/4) N} 2 (λ 2/4) and. At this _{time, N 1 D 1 = N 2} D 2 = (λ 1/4) × 3 = 730/4 ≒ 633/4 (= λ 2/4) ...... (7) Therefore, N ₁ ≒ 1.727 and N ₂ ≒ 1.483. Therefore, (6 ′) is expressed as 1.50 / 1.727 (633 nm / 4) −1.483 (633 nm / 4) / air (10) as shown by 104. . However, (10) does not strictly satisfy the condition of (5). That is, if N ₂ = 1.483, as indicated by 106, N ₁ = 1.816 for n _sub = 1.50.

By the way, the condition (5) is a condition of zero reflection, but depending on the type of anti-reflection, the wavelength λ ₁ or λ ₂
There is also a mild condition that the reflectance should be less than 1%, or that it should be less than the reflection of the substrate itself. In addition,
The exact complex amplitude reflectance graph of (6) is shown as 102 in FIG. The reflection characteristics of the (6), is as shown in FIG. 2, the reflectance at lambda ₁ is 0.25%. This corresponds to the root mean square of the refractive index. Strictly, as described above, the configuration of (6) is at 633 nm, and the solid line 100 in FIG.
It is an equivalent V coat as shown below. When N ₁ and N ₂ are obtained from FIG. ₁ , they are approximated by dotted lines 104 to, and N ₁ ≒ 1.88 and N ₂ ≒ 1.50.

Example (2) Visible / infrared two-wavelength region antireflection film (visible: λ ₁ = 430 to 6)
50 nm, infrared: λ ₂ = 3.0 to 5.0 μm) Here, of the visible range λ ₁ and the infrared range λ ₂ , the center wavelength 55
Select 0nm and 3750nm, 1.63 is the refractive index of Al ₂ O ₃ , 1.38 is
The refractive index of MgF ₂ , 1.46 is the refractive index of SiO ₂ , and 2.03 is the refractive index of ZrO ₂ .

The two-wavelength band anti-reflection coating of this configuration has a visible region (center wavelength of 550 nm) and an infrared region (center wavelength of 3.75 μm) which are relatively far apart.
m) has a sufficient antireflection effect.

 This will be described below.

This configuration also, in the lambda _2, the solid line 200 of FIG. 3
As shown in 204, N ₁ = 1.7
47, N ₂ = 1.420... (11 ′).

Example As a rough approximation (1) the total optical film thickness to think in the same manner as (lambda _1/4) × 12 next first half 1.63 (lambda _{1/4)
-2.03 (λ 1 /2)-1.63(λ 1 /4)-1.46(λ 1} /2) of the λ
_Two- substrate refractive index adjustment layer, latter half 1.46 (λ _1/2) -1.38 (λ ₁
/2)-1.63(λ considered _{1 /4)-1.38(λ 1/4)} to the lambda ₂ antireflective layer. At this _{time, N 1 D 1 = N 2} D 2 = (λ 1/4) × 6 = (550/4) × 6 = (3300/4) (3750/4) = (λ 2/4) Therefore, N ₁ ≒ 1.675 and N ₂ ≒ 1.433. Therefore, the approximation of (11) is, as shown by 206, 1.42 / 1.675 (3750 nm / 4) −1.433 (3750 nm / 4) / air …… (12) Although this does not strictly satisfy the condition (5), the reflection characteristic of (11) is as shown in FIG. 4 and can be used practically as an antireflection film. The exact complex amplitude reflectance graph of (11) is shown as 202 in FIG.

[Brief description of the drawings]

FIG. 1 is a graph of complex amplitude reflectance by Apfel display of the first embodiment of the present invention, FIG. 2 is a reflection characteristic diagram of the first embodiment,
FIG. 3 is a graph of complex amplitude reflectance in Apfel display of the second embodiment, FIG. 4 is a reflection characteristic diagram of the second embodiment, and FIGS. 5 and 6 are graphs of complex amplitude reflectance in Apfel display. FIG. 10: a graph showing a region with a reflectance of 1% 12: a graph showing a region with a reflectance of 0.5% 14: wavelength ratio 1.1 16 wavelength ratio 1.2 18 wavelength ratio 1.3 100 of the first embodiment Complex amplitude reflectance graph 200: complex amplitude reflectance graph of the second embodiment

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References Industrial Technology Institute Osaka Industrial Technology Laboratory Report No. 315 “Study of antireflection film” by Tsukasa Sawaki (September 1960), pp. 36-44

Claims (1)

(57) [Claims] _1. A first substrate refractive index adjusting layer having a refractive index n ₁ and a thickness d ₁ with respect to a center wavelength λ ₁ on a substrate S having a refractive index n _{sub, and} a first refractive index adjusting layer having a refractive index n ₂ and a thickness d ₂ . sequentially laminated one antireflection _{layer, n 1 d 1 ≒ λ 1} /4, n 2 d 2 ≒ λ 1/4, In the film configuration of the antireflection film that satisfies the following relational expression, at least one portion between the substrate S and the first substrate refractive index adjustment layer and between the first substrate refractive index adjustment layer and the first antireflection layer has a refractive index of: n _A ,
n _B, with respect to materials of n _C, n an integer multiple of _{A (λ 1/2),} or n
_{B (λ 1/4) -n} C (λ 1/2) either one of _{-n B (λ 1/4)} , or an anti-reflection film arranged non involvement layer with respect to the wavelength lambda ₁ consisting of combinations The non-participating layer and the first
A multilayer film composed of a substrate refractive index adjusting layer and a first antireflection film is formed such that a center wavelength λ ₁ and a center wavelength λ ₂ (2λ
₁ <λ ₂ ), the total optical film thickness is divided into approximately two equal parts, the refractive indices of the first half and the second half are N ₁ and N ₂ , and the film thickness is D ₁ ,
When the _{D 2, N 1 D 1 ≒} λ 2/4, N 2 D 2 ≒ λ 2/4, Satisfying the following relational expression, the center wavelength λ ₁ in the ultraviolet region:
Central wavelength lambda _2, or visible infrared region two wavelengths band antireflection film, which prevents reflection of the two-wavelength region of the central wavelength lambda ₂ with respect to the central wavelength lambda ₁ of the visible range with respect.