JP2007183379A - Optical multilayer film and method for producing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical multilayer film having excellent polarized light separation characteristics and free of film cracking and a method for producing the same. <P>SOLUTION: A first dielectric film group 110 obtained by alternately stacking a low-refractive-index film 111 and an insertion film 112 comprising a high-refractive-index film and a medium-refractive-index film or an insertion film 112a comprising at least one of a high-refractive-index film and a medium-refractive-index film is formed on a substrate 101 by way of an underlayer 102. A second dielectric film group 120 obtained by alternately stacking a low-refractive-index film 121 and a high-refractive-index film 122 is formed on the first dielectric film group 110. A two-layer structure obtained by joining an MgF<SB>2</SB>film having tensile stress and an SiO<SB>2</SB>film having compressive stress is provided to each low-refractive-index film 111 in the first dielectric film group 110 to relieve the internal stress of the film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a polarization beam splitter (PBS) mounted on a liquid crystal projector or the like, and has polarization separation characteristics of S-polarized light transmission, P-polarized light reflection in the visible blue band, and S-polarized light reflection and P-polarized light transmission in the red band. The present invention relates to an optical multilayer film and a method for manufacturing the same.

  2. Description of the Related Art Conventionally, a polarization beam splitter used for a liquid crystal projector or the like is configured by providing a dielectric multilayer film (polarization separation film) on a joint surface of a prism as described in Patent Document 1. This polarization separation film is composed of alternating layers of a high refractive index film and a low refractive index film, and has high S-polarized reflectance and high P-polarized transmittance characteristics in the visible range.

  Further, as described in Patent Document 2, the color separation optical filter is composed of a laminated structure in which at least three kinds of dielectric films having different refractive indexes are combined and repeatedly stacked with an optical film thickness λ / 4. There are also examples. This filter has high S-polarized reflectance and high P-polarized reflectance characteristics in a specific wavelength band.

  In addition, as an application example of the polarization beam splitter, when the edges (short wavelength side) of the reflection bands of P-polarized light and S-polarized light overlap, the reflectance of the reflection bands of P-polarized light and S-polarized light is substantially equal. It is shown in Document 1.

When the color separation optical filter is composed of alternating layers of a high refractive index film and a low refractive index film, it is known that a material having a large refractive index difference can be configured with a smaller number of layers. An optical multilayer film by ion beam assisted deposition is disclosed. In this multi-layer film, TiO ₂ film as a high refractive index film, using a MgF ₂ film as a low refractive index film, is to laminate to relax the stress by ion beam assist method.
Japanese Patent Laid-Open No. 11-023842 Japanese Patent Laid-Open No. 07-168017 Japanese Patent No. 2530461 "Thin-film optical filters" (Angus Macleod) November 1989 Nikkan Kogyo Shimbun, Ltd. P403-P409

  The multilayer film configuration disclosed in Patent Document 1 uses an alternating layer of a high refractive index film and a low refractive index film to efficiently separate an S component and a P component over the entire visible band. However, in a specific wavelength band, for example, the red band and the blue band excluding the green band, it is not possible to efficiently separate the S component and the P component.

  The multilayer film configuration of Patent Document 2 realizes high S-polarized reflectance and high P-polarized reflectance characteristics in a specific wavelength band by repeatedly stacking three types of dielectric films with an optical film thickness λ / 4. However, the S component and the P component cannot be efficiently separated in a specific wavelength band.

Non-Patent Document 1 shows a film configuration of (MLMH) ^{n where} M is the intermediate refractive index, L is the low refractive index, H is the high refractive index, and n is the number of repetitions of the four-layer stack. . This is a case where the reflectances of the P-polarized light and the S-polarized light are equal, and an example having a high S-polarized light transmittance and a high P-polarized light reflectance characteristic in a specific wavelength band is not disclosed.

  In Patent Document 3, film breakage can be prevented by using the ion beam assist method, but at the same time, the magnesium fluoride film is damaged and cannot be absorbed.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has a polarization separation characteristic that efficiently separates P-component light and S-component light in the visible blue and red bands. It is an object of the present invention to provide a high-quality optical multilayer film and a method for producing the same.

  In order to achieve the above object, the optical multilayer film of the present invention comprises a high refractive index film having a refractive index of 2.0 or more, an intermediate refractive index film having a refractive index of 1.5 or more and less than 2.0, and a refractive index. An alternating multilayer film including a low refractive index film of less than 1.5, wherein the low refractive index film includes a first low refractive index layer having a tensile stress and a second low refractive index layer having a compressive stress. And a laminated structure in which the two are joined together.

By the stacked structure formed by joining SiO ₂ film having a MgF ₂ film and the compressive stress of the tensile stress, preventing the film cracking in the low refractive index film, S-polarized light transmittance in the blue band in the visible range, P-polarized light reflected red In the band, a high-quality optical multilayer film having polarization separation characteristics of S-polarized light reflection and P-polarized light transmission can be realized.

Furthermore, by interposing an SiO ₂ film that prevents damage (absorption) to the MgF ₂ film, the ion beam assist method can be applied to the intermediate refractive index film and the high refractive index film. Thereby, the stress can be further relaxed.

  The best mode for carrying out the present invention will be described with reference to the drawings.

As shown in FIG. 1, a high refractive index film H having a refractive index of 2.0 or more, an intermediate refractive index film M having a refractive index of 1.5 or more and less than 2.0, and a refractive index of 1 on a substrate 101. A first dielectric film group (alternate multilayer film) 110 in which a low refractive index film L of less than 0.5 is stacked in the order of HMHL (or HLHM). Each low refractive index film 111 includes a first low refractive index layer L ₁ having a tensile stress, the second low refractive index layer having a first compressive stress formed in contact with the low refractive index layer L ₁ L which is constituted by two layers of _2.

  In the base structure HMHL of the first dielectric film group 110, the insertion film 112 inserted between the low refractive index films 111 has three layers including the intermediate refractive index film M and the high refractive index film H, or a single layer. The insertion film 112a includes a configuration in which an intermediate refractive index film M or a high refractive index film H is inserted therebetween. Alternatively, an intermediate refractive index film M and a high refractive index film H may be used as a two-layer insertion film.

  Further, a second dielectric film group (alternate multilayer film) 120 in which low refractive index films 121 (or intermediate refractive index films) and high refractive index films 122 are alternately stacked is provided. The second dielectric film group 120 may be provided in contact with the substrate side of the first dielectric film group 110 or may be provided at the interface opposite to the substrate side, but preferably opposite to the substrate side. It is more convenient in terms of stress control to include the second dielectric film group 120 at the side interface.

  Further, the final layer has an intermediate refractive index film (not shown), and is joined by a high refractive index prism (refractive index of 1.8 or more) through the intermediate refractive index film.

First low refractive index layer MgF ₂ film as L _1, a second low refractive index layer L ₂ is optimum SiO ₂ film, TiO ₂ film as a high refractive index film H, Nb ₂ O ₅ film A Ta ₂ O ₅ film or the like can be used. As the intermediate refractive index film M, an Al ₂ O ₃ film is optimal.

The multilayer film structure according to the present embodiment aims to obtain polarization separation characteristics of S-polarized light transmission and P-polarized light reflection in the visible blue band and S-polarized light reflection and P-polarized light transmission in the red band. For this purpose, the geometrical film thickness of one layer of MgF ₂ is preferably 40 nm or more, and the total of the laminated geometric film thicknesses is preferably 600 nm or more. The film thickness of SiO ₂ preferably has a geometric thickness of 20 nm or more from the viewpoint of stress control and prevention of damage (absorption) to MgF ₂ during ion beam assist.

  For stress control, the ion beam assist method is preferably used, and can be used for the insertion film of the first dielectric film group or the second dielectric film group.

In the above configuration, the larger the layer thickness and the number of layers of the MgF ₂ film that is the first low refractive index layer, the better the polarization separation characteristics tend to be. On the other hand, film cracking tends to occur. It is possible to estimate the total stress of the laminated film from the stress of each single film, and it is possible to predict the occurrence of approximate film cracking. As a result of investigation, in a multilayer film configuration using a total of 600 nm or more of MgF ₂ film, it is necessary to suppress the total stress (predicted film cracking limit total stress) to 300 N / m or less.

  By using a low refractive index film composed of a first low refractive index layer having a tensile stress and a second low refractive index layer having a compressive stress, the total stress is alleviated without impairing the characteristics of the optical multilayer film. Film cracking can be prevented. In order to relieve stress, the thickness of the second low refractive index layer needs to be 20 nm or more.

  In the laminated structure in which the insertion film provided between the low refractive index films is formed of three or less layers of the intermediate refractive index film and the high refractive index film, and the low refractive index film and the insertion film are alternately provided, By alternately repeating the insertion film including the thin high refractive index film, a high P-polarized light reflectance can be obtained.

In the optical multilayer film including the MgF ₂ film, the stress of the multilayer film varies depending on the film configuration (material, number of layers, film thickness, film formation conditions), but the total geometric thickness of the MgF ₂ film is 600 nm. In such a case, it is effective to use a SiO ₂ film in order to prevent film cracking.

The first role of the SiO ₂ film is to alleviate the stress of the MgF ₂ film, a second role is to obtain the spectral characteristics of interest, the third role when using the ion beam assisted deposition , To prevent the MgF ₂ film from being damaged (absorbed) by the ion beam. For this purpose, the film thickness of SiO ₂ needs to be 20 nm or more. Here, the purpose of using ion beam assist is to reduce the number of layers by obtaining stress relaxation and obtaining a high refractive index film having a higher refractive index.

  A second alternating multilayer film composed of a high refractive index film and a low refractive index film or a high refractive index film and an intermediate refractive index film is provided in contact with the substrate side or the interface on the opposite side of the substrate side. In the configuration in which the prism is bonded via the refractive index film, the S-polarized light transmittance in the red region can be suppressed.

As a substrate, a PBH56 (refractive index 1.84) prism is used, and an optical multilayer of 84 layers having polarization separation characteristics of S-polarized light transmission, P-polarized light reflection in the visible blue band, S-polarized light reflection, and P-polarized light transmission in the red band. The film was formed by vacuum deposition at a substrate heating temperature of 270 ° C. Table 1 shows the film configuration of this example. Here, d indicates the geometric film thickness. TiO ₂ (refractive index 2.35) for the high refractive index film, Al ₂ O ₃ (refractive index 1.62) for the intermediate refractive index film, and MgF ₂ (refractive index 1.30) for the first low refractive index layer. 38), SiO ₂ (refractive index 1.46) was used for the second low refractive index layer.

After forming the base layer on the substrate, a low-refractive index film including a first low-refractive index layer and a second low-refractive index layer formed in contact with the first low-refractive index layer is formed from the substrate side. . Next, an insertion film made of at least one of a TiO ₂ film and an Al ₂ O ₃ film is formed in contact with the low refractive index film. The first dielectric film group was formed by alternately repeating these two steps. Further, a high refractive index film and a low refractive index film were alternately laminated to form a second dielectric film group having layer numbers 2 to 9.

  FIG. 2 is a graph showing the film characteristics of Example 1. The vertical axis represents transmittance (%), the horizontal axis represents wavelength, and the characteristics of P-polarized light (Tp) and S-polarized light (Ts) when the incident angle in the prism is 45 degrees.

In the film configuration of Example 1, the total thickness of the MgF ₂ film as the first low refractive index layer is 680 nm, but the stress is relaxed by the total thickness of 1268 nm of the SiO ₂ film as the second low refractive index layer. It is considered that no film cracking occurred. At this time, the predicted total stress was approximately 290 N / m, which was in the vicinity of the predicted film cracking limit total stress. From the viewpoint of film cracking, it is preferable that the total thickness of the MgF ₂ film is thin.

In the same manner as in Example 1, an 84-layer optical multilayer film having polarization separation characteristics was formed at a substrate heating temperature of 150 ° C. As the high refractive index film, a TiO ₂ film (refractive index: 2.45) by an ion beam assist method was used, and as the intermediate refractive index film, an Al ₂ O ₃ film (refractive index: 1.64) by an ion beam assist method was used. Table 2 shows the film configuration.

After forming the base layer on the substrate, a low refractive index film comprising a first low refractive index layer and a second low refractive index layer formed in contact with the first low refractive index layer from the substrate side is vacuum deposited. Form by law. Next, an insertion film made of at least one of a TiO ₂ film and an Al ₂ O ₃ film is formed in contact with the low refractive index film by an ion beam assist method. These two steps were alternately repeated to form a first dielectric film group. Furthermore, a second dielectric film group consisting of layer numbers 2 to 9 was formed by alternately laminating a high refractive index film by an ion beam assist method and a low refractive index film by a vacuum deposition method.

In Table 2, IADTiO ₂ and IADAl ₂ O ₃ indicate a TiO ₂ film and an Al ₂ O ₃ film formed by an ion beam assist method, both of which are formed under the conditions of an acceleration voltage of 750 KV and a current density of 20 μA / cm ^2. Filmed.

The minimum film thickness of the SiO ₂ film, which is the second low refractive index layer, was set to 30 nm in order to prevent damage to the MgF ₂ film when forming the TiO ₂ film by the ion beam assist method.

  FIG. 3 shows the film characteristics of Example 2. The vertical axis represents transmittance (%), the horizontal axis represents wavelength, and the characteristics of P-polarized light (Tp) and S-polarized light (Ts) when the incident angle in the prism is 45 degrees.

In the film configuration of Example 2, the total thickness of the MgF ₂ film as the first low refractive index layer is 1190 nm, but the SiO ₂ film as the second low refractive index layer and TiO ₂ by the ion beam assist method are used. _It is considered that the stress was relaxed by the _two films and the Al ₂ O ₃ film and no film cracking occurred. At this time, the predicted total stress was approximately 110 N / m, which was below the predicted total film cracking limit total stress. Further, the absorption of S-polarized light in the blue region (420 to 480 nm) was about 1%, and the polarization separation characteristic was also improved from that of Example 1.

(Comparative Example 1)
A 63-layer optical multilayer film having polarization separation characteristics was formed by vacuum deposition. However, the low refractive index film was formed only with the MgF ₂ film as the first low refractive index layer. The film configuration is shown in Table 3, and the film characteristics are shown in FIG. Similar to Example 1, the characteristics of P-polarized light (Tp) and S-polarized light (Ts) when the incident angle in the prism is 45 degrees. Although the total thickness of the MgF ₂ film was as thick as 1582 nm, the polarization separation characteristics were improved with a small number of 63 layers. Further, the absorption of S-polarized light in the blue region (420 to 480 nm) was about 1%, and there was no problem in optical characteristics. However, since the stress of the MgF ₂ film is large, the multilayer film is cracked and cannot be practically used. At this time, the predicted total stress was approximately 880 N / m, which was much higher than the predicted total film cracking limit total stress.

(Comparative Example 2)
As in Example 2, a 79-layer optical multilayer film having polarization separation characteristics was formed at a substrate heating temperature of 150 ° C. As the high refractive index film, a TiO ₂ film (refractive index 2.45) by an ion beam assist method was used, and as the intermediate refractive index film, Al ₂ O ₃ (refractive index 1.64) by an ion beam assist method was similarly used. Table 4 shows the film configuration. The minimum film thickness of the SiO ₂ film as the second low refractive index layer was 15 nm. FIG. 5 shows the film characteristics of Comparative Example 2. The vertical axis represents transmittance (%), the horizontal axis represents wavelength, and the characteristics of P-polarized light (Tp) and S-polarized light (Ts) when the incident angle in the prism is 45 degrees.

In the film configuration of Comparative Example 2, the total thickness of the MgF ₂ film as the first low refractive index layer is 1305 nm, but the SiO ₂ film as the second low refractive index layer and TiO ₂ by the ion beam assist method are used. _It is considered that the stress was relieved by the _two films and the Al ₂ O ₃ film and no film cracking occurred. At this time, the predicted total stress was approximately 120 N / m, which was below the predicted total film cracking limit total stress.

Further, the polarization separation characteristics were also improved as compared with Example 2. However, the absorption of S-polarized light in the blue region (420 to 480 nm) is about 2%, and improvement is desired. This is a little in order to prevent damage (absorption) to the MgF ₂ film when forming the TiO ₂ film by the ion beam assist method when the minimum film thickness of the SiO ₂ film as the second low refractive index layer is 15 nm. Presumed to be due to a lack. Therefore, it is considered that 20 nm or more is necessary as the minimum film thickness of the SiO ₂ film which is the second low refractive index layer.

It is a figure which shows the multilayer film structure by one embodiment. FIG. 3 is a diagram illustrating optical characteristics of the optical multilayer film of Example 1. FIG. 6 is a diagram showing optical characteristics of the optical multilayer film of Example 2. 6 is a diagram showing optical characteristics of an optical multilayer film of Comparative Example 1. FIG. It is a figure which shows the optical characteristic of the optical multilayer film of the comparative example 2.

Explanation of symbols

101 Substrate 110 First Dielectric Film Group 111, 121 Low Refractive Index Film 112, 112a Insertion Film 120 Second Dielectric Film Group

Claims (7)

  Alternating multilayer film comprising a high refractive index film having a refractive index of 2.0 or more, an intermediate refractive index film having a refractive index of 1.5 or more and less than 2.0, and a low refractive index film having a refractive index of less than 1.5 And the low refractive index film has a laminated structure in which a first low refractive index layer having tensile stress and a second low refractive index layer having compressive stress are joined. Multilayer film.   The alternating multilayer film has a multilayer film structure in which low-refractive index films having the stacked structure and three or less layers, and each layer is alternately stacked with an insertion film made of an intermediate refractive index film or a high refractive index film. The optical multilayer film according to claim 1. The first low refractive index layer is an MgF ₂ film, the total geometric thickness of all MgF ₂ films is 600 nm or more, and the second low refractive index layer is an SiO ₂ film, 3. The optical multilayer film according to claim 1, wherein the geometric thickness of each SiO ₂ film is 20 nm or more.   The low-refractive index film having a laminated structure is a low-refractive index film having a two-layer structure formed in order of the first low-refractive index layer and the second low-refractive index layer from the substrate side. The optical multilayer film according to any one of claims 1 to 3.   Having a second alternating multilayer film in which a high refractive index film and a low refractive index film, or a high refractive index film and an intermediate refractive index film are alternately laminated in contact with the substrate side or the interface opposite to the substrate side; The final layer of the second alternating multilayer film is an intermediate refractive index film, and is configured to be prism-bonded through the intermediate refractive index film. The optical multilayer film according to Item. Alternating film including a high refractive index film having a refractive index of 2.0 or more, an intermediate refractive index film having a refractive index of 1.5 or more and less than 2.0, and a plurality of low refractive index films having a refractive index of less than 1.5 In a method for producing an optical multilayer film having a multilayer film,
A first step of forming a low refractive index film having a laminated structure including a first low refractive index layer having a tensile stress and a second low refractive index layer having a compressive stress by a vacuum deposition method;
A second step of forming, by an ion beam assist method, an insertion film comprising three or more layers, each layer being an intermediate refractive index film or a high refractive index film, in contact with the low refractive index film having a laminated structure,
A method for producing an optical multilayer film, wherein the first and second steps are alternately repeated to form an alternate multilayer film.   7. The optical multilayer film according to claim 6, further comprising a third step of forming a second alternating multilayer film comprising a high refractive index film and a low refractive index film, or an intermediate refractive index film and a low refractive index film. Manufacturing method.

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