JPH0593811A - Light absorptive film - Google Patents

Abstract

PURPOSE:To obtain the high-quality light absorptive film which lessens the generation of stresses and does not crack by forming the film of the specific layer of the light absorptive film by using SiO2. CONSTITUTION:The stresses of the film of MgF2 are offset and the generation of cracks is prevented by using the SiO2 as a dielectric film. The difference between a phase of a ray A emitted from the film and a phase of a ray B passing a binder is required to be set at 1/4lambda in the case of use for a phase film having 1/4lambda phase difference and, therefore, the MgF2 is not completely formed of the SiO2 but if the number M of the films to be laminated is an even number, the film of the (M/2)+ or -n [where n=0, 1, 2,...,{(M/2)-2}]th layer is formed of the {SiO2 and if the number M is an odd number the film of the {(M+1)/2)+ or -n} [where n=0, 1, 2,...{[M+1)/2],-2)}]th layer is formed of the SiO2. The stresses generated by the MgF2 in the first half of the films are offset by the central part of the films and the light absorptive film which is suppressed in the film thickness over the entire part and is easily workable is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection light absorbing film used as an ND filter, a phase plate for a phase contrast microscope, a pupil modulation filter for modulation contrast, and other pupil modulation filters.

[0002]

2. Description of the Related Art As a light absorbing film of this type, (1) as shown in JP-A-57-195207, it contains a dielectric film and a metal film and has an antireflection effect when used alone. Two multi-layered films that have another dielectric film sandwiched between them,
(2) As shown in Japanese Examined Patent Publication No. 55-47361, there is known one formed by alternately laminating a metal film and a dielectric film.

Further, due to the thin film processing technology, stress is generated in the thin film, but in a multilayer film in which a high refractive index material and a low refractive index material are alternately laminated, a material that produces compressive stress and tensile stress is generated. It is known that the stress is canceled by combining them (Fujiwara ed. "Optical thin film", Kyoritsu Shuppan Co., Ltd.)
Issue).

[0004]

By the way, the above (1)
In this case, since only two metal films are used, it is very difficult to make the spectral transmittance uniform and the reflectance small. Further, in the case of the above (2), if a metal film made of Ti or Cr and a transparent film made of MgF ₂ are used, a film having a uniform spectral transmittance and a small reflectance can be designed, but the number of laminated layers is large. There is a problem that the total thickness of the film becomes thicker and cracks are easily generated due to the stress of the film. Particularly in the case of a phase film, the light rays A and B as shown in FIG.
Since the phase difference is designed to be 1 / 4λ, the film thickness is further increased.

When used as a coat for a phase film or the like, the substrate temperature cannot be raised to 120 ° C. or higher because a pattern is formed using a resist or the like and then vacuum deposition is performed, so that cracks are likely to occur. Will be.

Therefore, a method of canceling the stress of the whole film by the tensile stress and the compressive stress of the film using a substance as shown in FIG. 2 is disclosed. In order to design a phase film having a phase difference, a film having a high refractive index must be used in combination, and only a thick film that is difficult to process can be designed.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to reduce the thickness of the film without causing cracks. An object of the present invention is to provide a light absorbing film for antireflection that can be used as a filter, a phase plate for a phase contrast microscope, a modulation contrast pupil modulation filter, and other pupil modulation filters.

[0008]

In order to achieve the above object, the light absorbing film according to the present invention comprises the following light absorbing film in which a dielectric film and a metal film are laminated. That is,
When the number of films to be laminated is M, and the total number of films is an even number, (M / 2) ± n (where n = 0, 1, 2, ...,
One of the {(M / 2) -2}] layer films is formed of SiO ₂ . If the total number of films is odd, {(M +
1) / 2} ± n (however, n = 0, 1, 2, ...
Any one of the {[(M + 1) / 2] -2}] layer films is Si.
It is formed of O ₂ . Alternatively, at least one layer of the laminated dielectric films is made of cryolite.

[0009]

When a light absorption film having a uniform spectral transmittance for preventing reflection is designed by using Ti or Inconel, the film has a structure in which dielectric films having a low refractive index and metal films are alternately laminated, and in particular, 7 Good characteristics can be obtained by using a multilayer film having more layers. In this case, MgF ₂ is often used for the dielectric film, but M
Since gF ₂ has a large film stress as shown in FIG. 2, when the total film thickness is designed to be large, cracks are likely to occur in the film. Therefore, as shown in FIG. 2, by using SiO ₂ which causes less stress in the film, MgF ₂
It is possible to cancel the stress of the film.

However, if this is used for a phase film having a phase difference of 1 / 4λ, as shown in FIG. 1, the phase between the phase of the light ray A that exits the film and the phase of the light ray B that passes through the bonding agent is increased. Since the difference must be 1 / 4λ, M
If all gF ₂ is SiO ₂ , the difference between the refractive index of the film and the refractive index of the bonding agent becomes small, resulting in a thick film. Therefore, when the number of films to be stacked is M near the center of the film, that is, (M /
2) ± n [however, n = 0, 1, 2, ..., {(M / 2)
-2}] layer film, or {(M +
1) / 2} ± n (however, n = 0, 1, 2, ...
By forming the film of the {[(M + 1) / 2] -2}] layer with SiO ₂ , the stress generated in MgF ₂ in the first half of the film can be canceled at the center of the film, and the entire film can be canceled. It is possible to form a light-absorbing film that is not too thick and is easy to process.

Although cryolite (Na ₃ AIF ₆ ) has a deliquescent property because it contains Na in its molecule,
Since the stress generation is much smaller than that of MgF ₂ (see FIG. 2), if at least one layer of the dielectric film is made of cryolite, the MgF will increase even if the total film thickness is increased or the number of layers is increased. ₂
Cracks are less likely to occur as compared with the film using. or,
When cryolite is used as the phase film, it is preferable to use a bonding agent to sandwich the entire film with a glass plate to prevent water from entering the film.

[0012]

EXAMPLE 1 A light absorbing film is composed of 9 layers using Ti, MgF ₂ and SiO ₂ , and the entire film is made of a bonding agent having a refractive index n = 1.56 and a refractive index n = 1. It was sandwiched between the substrate glass of 0.516 and the glass plate, and the phase difference was set to 1 / 4λ (see FIG. 1). The components, the thickness d, the refractive index n, and the transmittance T of light having a wavelength of 550 nm of each of the layers 1 to 9 sequentially laminated on the substrate glass are as follows. Layer component d n T (%) 1 MgF ₂ 286.4 1.37914 2 Ti 70.9 3 MgF ₂ 77.6 1.37914 4 Ti 48.9 5 SiO ₂ 70.9 1.460196 6 Ti 48.9 7 MgF ₂ 77.6 1.37914 8 Ti 70.9 9 MgF ₂ 286.4 1.37914 The structure of the light absorbing film was antireflection on both sides by making the film structure on the incident side and the emitting side symmetrical. .. 25% transmittance
When the following light-absorbing films are anti-reflection on both sides, it is better to have 9 or more layers. The spectral characteristics are as shown in FIG.

Example 2 The light absorbing film was composed of 11 layers using Ti, MgF ₂ and SiO ₂ , and the whole structure was the same as in Example 1. The components of each layer, the thickness d, the refractive index n, and the transmittance T are as follows. Layer component d n T (%) 1 MgF ₂ 314.5 1.37914 2 Ti 57.7 3 MgF ₂ 80.3 1.37914 4 Ti 31.4 5 SiO ₂ 81.7 1.46019 6 Ti 31.4 7 SiO ₂ 81.7 1.46019 8 Ti 31.49 MgF ₂ 80.3 1.37914 10 Ti 57.7 11 MgF ₂ 314.5 1.37914 The fifth layer and the seventh layer are formed of SiO ₂ . As a result, the characteristics of the light absorbing film are improved. Especially, the transmittance of the light absorption film is 15
%, The total film thickness becomes large. Therefore, cracks are less likely to occur when the number of stacked layers is about 11 layers. The spectral characteristics are as shown in FIG.

Example 3 The light absorbing film was composed of 11 layers using Inconel and cryolite, and the whole structure was the same as in Example 1. The components of each layer, the thickness d, the refractive index n, and the transmittance T are as follows. Layer component d n T (%) 1 Cryolite 224.2 1.371 2 Inconel 70.9 3 Cryolite 64.8 1.371 4 Inconel 58.4 5 Cryolite 37.4 1.371 16 Inconel 58.4 7 Cryolite 37.4 1.371 8 Inconel 58.4 9 Cryolite 64.8 1.371 10 Inconel 70.9 11 Cryolite 224.2 1.371 The spectral characteristics are shown in FIG. On the street.

[0015] Example 4 the light absorbing film is consisted 11 layers using Ti and MgF ₂ and SiO _2, the fifth layer and the seventh layer of Example 2 and MgF _2, also the third layer and the ninth A film according to this example was formed by using SiO ₂ as a layer. The components of each layer, the thickness d, the refractive index n, and the transmittance T are as follows. Layer component d n T (%) 1 MgF ₂ 400 1.37914 2 Ti 65.9 3 SiO ₂ 74.89 1.46019 4 Ti 47.4 5 MgF ₂ 93.94 1.37914 6 Ti 47.4 7 MgF ₂ 93.94 1.37914 8 Ti 47.4 9 SiO ₂ 74.89 1.46019 10 Ti 65.9 11 MgF ₂ 400. 1.37914 In the case of forming a thicker light absorbing film, the stress can be further reduced by inserting the SiO ₂ film at the position where the refractive index n is large. This embodiment corresponds to the case where the refractive index n is 3. The spectral characteristics are as shown in FIG.

Example 5 The light absorption film is composed of 13 layers using Ti, MgF ₂ and SiO ₂ . The components of each layer, the thickness d, the refractive index n, and the transmittance T are as follows. Layer component d n T (%) 1 MgF ₂ 250 1.37914 2 Ti 67.9 3 SiO ₂ 83.48 1.46019 4 Ti 67.9 5 MgF ₂ 140.84 1.37914 6 Ti 67.97 MgF ₂ 87.07 1.37914 8 Ti 67.9 9 MgF ₂ 140.84 1.37914 10 Ti 67.9 11 SiO ₂ 83.48 1.46019 12 Ti 67.9 13 MgF ₂ 250. 1.37914 In this embodiment, the refractive index n is 4. The spectral characteristics are as shown in FIG.

[0017]

As described above, according to the present invention, it is possible to provide a high-quality light-absorbing film in which stress is not generated as a whole and cracks are not generated.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of a light absorption film according to the present invention.

FIG. 2 is a characteristic diagram showing the film thickness dependence of stress of thin films made of various substances.

FIG. 3 is a spectral characteristic diagram of a first embodiment of a light absorbing film according to the present invention.

FIG. 4 is a spectral characteristic diagram of a second embodiment of the light absorbing film according to the present invention.

FIG. 5 is a spectral characteristic diagram of a light absorbing film according to a third embodiment of the present invention.

FIG. 6 is a spectral characteristic diagram of a light absorbing film according to a fourth embodiment of the present invention.

FIG. 7 is a spectral characteristic diagram of a fifth embodiment of the light absorbing film according to the present invention.

Claims (3)

[Claims] 1. A light absorbing film formed by stacking a dielectric film and a metal film, where M is the number of films to be stacked, and (M / 2) ± n
[However, n = 0, 1, 2, ..., {(M / 2) -2}]
A light absorbing film, characterized in that any one of the layers is formed of SiO ₂ . 2. A light-absorbing film formed by stacking a dielectric film and a metal film, where M is the number of films to be stacked, and {(M + 1) /
2} ± n [however, n = 0, 1, 2, ..., {[(M +
1) / 2] -2}]] A light-absorbing film, characterized in that any one of the layers is formed of SiO ₂ . 3. A light absorbing film formed by laminating a dielectric film and a metal film, wherein at least one layer of the dielectric film is made of cryolite.