JP6027199B2 - Phase difference element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a retardation element represented by a half-wave plate or a quarter-wave plate. More specifically, the present invention relates to a phase difference element that utilizes a difference in optical refractive index in the in-plane axial direction of light in a use band and a method for manufacturing the same.

  Conventionally, a retardation element is made of an inorganic optical single crystal such as quartz or a polymer stretched film. However, although the inorganic optical single crystal is excellent in performance, durability and reliability as a phase difference element, there are problems that raw material costs and processing costs are high and that the angle dependency with respect to incident light is relatively large. In addition, the polymer stretched film is the most commonly used retardation element, but has a drawback that it tends to deteriorate against heat and UV rays and has a problem in durability.

  Further, as the phase difference element, an oblique deposition film having an oblique columnar structure (an oblique deposition phase difference element) is known (see, for example, Patent Documents 1 to 3 and Non-Patent Document 1). In principle, the oblique deposition film can be set to have an arbitrary phase difference by adjusting the film thickness, and it is relatively easy to enlarge the area, and the cost may be reduced by mass production. Moreover, since an inorganic material is used, a retardation element excellent in light resistance and heat resistance can be provided.

JP 2001-228330 A JP 2006-171328 A JP 63-132203 A

Serial bideposition of anisotropic thin films with enhanced linear birefringence / APPLIED OPTICS / Vol. 38, No. 16/1 June 1999

As described above, although the retardation element using the obliquely deposited film is excellent in light resistance and heat resistance, a high refractive index substance such as Ta ₂ O ₅ , ZrO ₂ , or TiO ₂ is used as the deposition material. A large difference from the refractive index of the main transparent substrate, such as glass or quartz, causes reflection of incident light at the substrate / deposition film interface.

  The present invention has been proposed in view of such circumstances, and an object of the present invention is to provide a phase difference element capable of reducing reflection of incident light and a method for manufacturing the same.

  In order to solve the above-described problems, the retardation element according to the present invention is an oblique deposition in which a transparent substrate and a dielectric material are alternately obliquely deposited from two directions different from each other by 180 °, and the thickness of each layer is equal to or less than a use wavelength. And a three-layer dielectric layer in which a high refractive index film is sandwiched between two low refractive index films between the transparent substrate and the oblique vapor deposition film. The refractive index of the low refractive index film is 1 An interface antireflection film having a refractive index of less than 0.5, a refractive index of the high refractive index film of greater than 2.0, and a thickness of the high refractive index film of from 0.5 nm to 5 nm. 1. The average refractive index of the antireflection film is larger than the refractive index of the transparent substrate, smaller than the refractive index of the oblique vapor deposition film, and the refractive index in two directions of the oblique vapor deposition film is larger than 1.55. It is characterized by being in a range smaller than 7 and different from each other.

  In the method of manufacturing a retardation element according to the present invention, a low refractive index film and a high refractive index film are alternately laminated on a transparent substrate, and the high refractive index film is sandwiched between two low refractive index films. A low refractive index film comprising three dielectric layers, wherein the average refractive index of the three dielectric layers is larger than the refractive index of the transparent substrate and smaller than the refractive index of the obliquely deposited film formed next. An antireflective film having a refractive index of less than 1.5, a refractive index of the high refractive index film of greater than 2.0, and a thickness of the high refractive index film of 0.5 nm to 5 nm is formed. Dielectric materials are alternately obliquely deposited on the film from two directions different from each other by 180 °, and the refractive indexes in the two directions are in a range larger than 1.55 and smaller than 1.7. An oblique vapor deposition film having a wavelength shorter than the wavelength used is formed.

  Further, the liquid crystal projector according to the present invention includes a transparent substrate, an obliquely deposited film in which the dielectric material is alternately obliquely deposited from two directions different from each other by 180 °, and the thickness of each layer is equal to or less than a use wavelength, and the transparent substrate. And the obliquely deposited film are composed of three dielectric layers in which a high refractive index film is sandwiched between two low refractive index films, and the refractive index of the low refractive index film is smaller than 1.5, And an interface antireflection film having a refractive index greater than 2.0 and a high refractive index film having a thickness of 0.5 nm to 5 nm. The refractive index is larger than the refractive index of the transparent substrate, smaller than the refractive index of the oblique vapor deposition film, and the refractive index in two directions of the oblique vapor deposition film is larger than 1.55 and smaller than 1.7. There are different retardation elements between the polarizing beam splitter and the liquid crystal cell. And wherein the Rukoto.

  In addition, an optical apparatus according to the present invention includes a transparent substrate, an oblique vapor deposition film in which a dielectric material is alternately obliquely deposited from two directions different from each other by 180 °, and each layer has a thickness equal to or less than a use wavelength, and the transparent substrate. And the obliquely deposited film are composed of three dielectric layers in which a high refractive index film is sandwiched between two low refractive index films, and the refractive index of the low refractive index film is smaller than 1.5, And an interface antireflection film having a refractive index greater than 2.0 and a high refractive index film having a thickness of 0.5 nm to 5 nm. The refractive index is larger than the refractive index of the transparent substrate, smaller than the refractive index of the oblique vapor deposition film, and the refractive index in two directions of the oblique vapor deposition film is larger than 1.55 and smaller than 1.7. There are different phase difference elements.

  In the present invention, two low refractive indexes are formed between the transparent substrate and the oblique deposition film in which the dielectric material is alternately obliquely deposited from two directions different from each other by 180 ° and the thickness of each layer is equal to or less than the use wavelength. The high refractive index film comprises three dielectric layers with a high refractive index film sandwiched between films, the refractive index of the low refractive index film is smaller than 1.5, the refractive index of the high refractive index film is larger than 2.0, An interface antireflection film having a thickness of 0.5 nm to 5 nm, and an average refractive index of the interface antireflection film composed of the three dielectric layers is larger than a refractive index of the transparent substrate, Since the refractive index in the two directions of the oblique vapor deposition film is smaller than the refractive index and different from each other in a range larger than 1.55 and smaller than 1.7, reflection of incident light is reduced and optical characteristics are improved. be able to.

It is a schematic sectional drawing which shows the phase difference element which concerns on one embodiment of this invention. It is a flowchart which shows the manufacturing method of the phase difference element which concerns on one embodiment of this invention. It is a schematic sectional drawing which shows the structure of a part of optical engine used for a reflection type liquid crystal projector. It is a schematic diagram which shows the simulation model of the phase difference element in which the interface antireflection film is not formed. It is a graph showing the refractive index wavelength dispersion of a quartz substrate and Ta ₂ O ₅ oblique deposition film. It is a graph which shows the reflectance of the phase difference element in which the interface antireflection film is not formed. It is a schematic diagram which shows the simulation model of the phase difference element in which the interface reflection preventing film is formed. Al ₂ O ₃ interface anti-reflection film is a graph showing the refractive index wavelength dispersion of a quartz substrate and _Ta 2 _{O 5} oblique deposition film. Al ₂ O ₃ interface anti-reflection film is a graph showing the reflectance of a phase difference element is formed. SiO ₂ interface anti-reflection film is a graph showing the refractive index wavelength dispersion of a quartz substrate and _Ta 2 _{O 5} oblique deposition film. It is a graph showing the reflectance of the phase difference element SiO ₂ interface anti-reflection film is formed. Optimum interface anti-reflection film is a graph showing the refractive index wavelength dispersion of a quartz substrate and Ta ₂ O ₅ oblique deposition film. It is a graph which shows the reflectance of the phase difference element in which the optimal interface reflection prevention film was formed. It is a graph which shows the reflectance of an optimal interface antireflection film. It is a graph which shows the reflectance of a 3 layer structure film | membrane and an optimal interface antireflection film. Three-layer structure film 2.3nm thickness of the _Nb 2 _{O 5} film is a graph showing the reflectance when 3.3 nm, or a 4.3 nm. A second layer of three-layer structure is a graph showing the reflectance of the phase difference element when the the Al ₂ O ₃ film. A second layer of three-layer structure is a graph showing the reflectance of the phase difference element when the Nb ₂ O ₅ film. It is a graph which shows the reflectance of the phase difference element in which the interface antireflection film of 3 layer structure was formed, and the phase difference element in which the interface antireflection film was not formed. It is a graph which shows the reflectance of the phase difference element in which the interface antireflection film of the 3 layer structure was formed with respect to the refractive index of an oblique deposition film. It is a graph showing the reflectance of the phase difference element when varying the thickness of the first layer SiO ₂ film and the third layer SiO ₂ film of a three-layer structure. It is a schematic diagram which shows the structure of the phase difference element of an Example. It is a schematic diagram which shows the structure of the phase difference element of an Example. It is a graph which shows the wavelength dependence of retardation (Re). It is a graph which shows the wavelength dependence of the transmittance | permeability. It is a graph which shows the wavelength dependence of a reflectance. It is a graph which shows the reflectance of the phase difference element of an Example and a comparative example. It is a graph which shows the incident angle dependence of the retardation of the phase difference element of an Example. It is a graph which shows the incident angle dependence of the retardation of the phase difference element of an Example. It is a graph which shows the incident angle dependence of the retardation of the phase difference element of a comparative example. It is a schematic diagram for demonstrating the incident angle with respect to a phase difference element.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings.
1. 1. Configuration of phase difference element 2. Manufacturing method of phase difference element 3. Application example to liquid crystal projector Example

<1. Configuration of retardation element>
FIG. 1 is a schematic cross-sectional view showing a phase difference element according to an embodiment of the present invention. As shown in FIG. 1, a retardation element 1 includes a transparent substrate 11, an interface antireflection film 12 in which a high refractive index film and a low refractive index film are alternately stacked on the transparent substrate 11, and an interface antireflection film. An obliquely deposited film 13 that is alternately obliquely vapor-deposited so that the thickness of each layer is equal to or less than the working wavelength from two directions that are 180 ° different from each other in dielectric material, and a CVD formed on the obliquely deposited film 13 (Chemical Vapor Deposition) The dielectric film 14 is provided. Further, antireflection films 15A and 15B made of a laminated dielectric are provided on both the front and back surfaces.

  The transparent substrate 11 is made of a material having a refractive index of 1.1 to 2.2, such as glass, quartz, or quartz, that is transparent to the light in the use band. In the present embodiment, it is preferable to use quartz as the constituent material of the transparent substrate 11. Quartz has excellent heat resistance and a very low coefficient of thermal expansion, and its light transmittance is very high over all wavelengths from ultraviolet to infrared. Therefore, for example, quartz is particularly preferably used for a retardation element of a reflective liquid crystal projector.

  The interface antireflection film 12 is configured by alternately laminating a high refractive index film and a low refractive index film between the transparent substrate 11 and the oblique vapor deposition film 13. It functions as a matching film that reduces the reflection of incident light at the interface. It is difficult for the interface antireflection film 12 to satisfy both the surface property of the substrate and the refractive index having an antireflection effect only from a certain single layer material. Therefore, in the present embodiment, the reflectance is reduced by making the interface antireflection film 12 have two or more layers in which a high refractive index film and a low refractive index film are alternately laminated.

Also, interface anti-reflection film 12 is preferably film in contact with the oblique deposition film 13 is SiO _2. By making the uppermost part of the interface antireflection film 12 with SiO _{2 made of the} same material as that of the transparent substrate, fluctuations in the optical characteristics of the oblique deposition film 13 can be suppressed. The thickness of the SiO ₂ is preferably 60nm or more. By setting the film thickness of SiO ₂ to 60 nm or more, the oblique vapor deposition film 13 having excellent optical characteristics can be obtained. In the oblique deposition film 13, the optical characteristics such as birefringence greatly depend on the surface of the base material on which the film is formed. Therefore, at the oblique deposition film / substrate interface, a typical antireflection coating design is unique to the oblique deposition film. It is necessary to consider the effect.

  The refractive index of the interface antireflection film 12 is higher than the refractive index of the transparent substrate 11 and smaller than the refractive index of the oblique deposition film 13. Thereby, reflection of incident light can be reduced.

  More specifically, the average refractive index n of the interface antireflection film 12 is preferably in the relationship of the following formula (1).

Here, nsub is the refractive index of the transparent substrate 11, and _nob1x , _nobly ( _nob1x > _nobly ) is the refractive index of the two orthogonal axes x, y in the plane of the oblique deposition film 13, respectively.

  The refractive index of the interface antireflection film 12 is determined by the wavelength band using the retardation element. For example, when the reference wavelength is 550 nm, the refractive index of the glass substrate is 1.51, and the refractive index of the oblique deposition film is If it is about 1.63, a dielectric material corresponding to a refractive index of 1.53, which is an intermediate value between them, may be formed.

The interface antireflection film 12 has a three-layer structure in which a low refractive index film, a high refractive index film, and a low refractive index film are laminated in this order, and the refractive index nL of the low refractive index film is smaller than 1.5. The refractive index nH of the high refractive index film is preferably larger than 2.0. As such a high refractive index film, a high refractive material such as Nb ₂ O ₅ , TiO ₂ , LaTiO ₃ , or Ta ₂ O ₅ can be used.

In addition, when each of the refractive indexes n _oblx and n _obly (n _oblx > n _obly ) of the in-plane orthogonal two axes x and y of the oblique deposition film is in the range of 1.55 to 1.7, a three-layer structure The film thickness of the high refractive index film is preferably in the range of 0.5 to 5.5 nm. Thereby, a reflectance of 0.3% or less can be realized in the blue wavelength band (440 to 510 nm).

  The thickness of the three-layer interface antireflection film is preferably 90% or less of the design center wavelength. When the thickness of the interface antireflection film is 90% or less of the design center wavelength, the reflectance can be reduced.

  The obliquely deposited film 13 is obliquely deposited alternately from two directions whose dielectric materials are 180 ° different. It is known that oblique deposition causes in-film inhomogeneity (difference in refractive index between the initial and final film formation). The element provided with the laminated structure of the oblique vapor deposition film 13 has a high reflectance between the respective layers due to this refractive index difference. Further, this refractive index difference is proportional to the film thickness of each layer. Therefore, in this embodiment, by setting the thickness of each layer to be equal to or less than the use wavelength, it is possible to reduce the difference in refractive index within the layer and reduce reflection between the layers. Furthermore, the viewing angle dependency can be improved by setting the thickness of each layer to be equal to or less than the operating wavelength. Therefore, for example, when applied to a reflective liquid crystal projector, it is possible to improve the contrast of the projected image and reduce color unevenness and chromaticity deviation.

The dielectric material of the oblique deposition film 13 is preferably an oxide of Ta, Zr, Ti, Si, Al, Nb, or La, or a combination thereof. Specific examples of the dielectric material include Ta ₂ O ₅ , ZrO ₂ , TiO ₂ , and Ta ₂ O _{5 in} which ₅ to 15 wt% of TiO ₂ is added. By using such a dielectric material, the in-plane orthogonal biaxial x and y refractive indexes n _oblx and n _obly (n _oblx > n _obly ) are each 1.55 to 1.7 It becomes possible to obtain a vapor deposition film.

  The CVD dielectric film 14 is a highly dense film and can be obtained by film formation by the CVD method. By forming this CVD dielectric film 14, it is possible to prevent moisture in the atmosphere from entering and exiting the obliquely deposited film 13.

  The antireflection films (AR films) 15A and 16B are multilayer thin films composed of, for example, a high refractive index film and a low refractive index film, and prevent surface reflection and improve transparency.

  According to the phase difference element having such a configuration, the reflection of incident light can be reduced and the viewing angle dependency can be improved.

<2. Manufacturing method of retardation element>
Next, a method for manufacturing the retardation element in the present embodiment will be described. FIG. 2 is a flowchart showing a method of manufacturing a retardation element according to an embodiment of the present invention.

First, in step S1, a laminated dielectric film is formed as an interface antireflection film on a transparent substrate by sputtering, CVD, vapor deposition, or the like. As the dielectric, an oxide such as Ta, Zr, Ti, Si, Al, Nb, and La, a fluoride of Mg, or a combination thereof can be used. Then, the interface antireflection film 12 having an intermediate value between the refractive index of the transparent substrate 11 and the refractive index of the oblique deposition film 13 is obtained. The uppermost film in contact with the oblique deposition film 13 of the interface antireflection film 12 is preferably SiO ₂ .

  In step S2, a high refractive index material is formed on the interface antireflection film 12 by oblique vapor deposition. Specifically, the oblique deposition film 13 composed of multiple layers with different film forming directions is formed by rotating the transparent substrate 11 180 degrees in the in-plane direction every time the film is formed. At this time, a multilayer structure in which the film thickness per layer is equal to or less than the wavelength is adopted. Further, the obliquely deposited film may be filled with a low refractive index substance (23) JP 2012-242449 A 2012.12.10 for the purpose of improving moisture resistance. As the high refractive index material, an oxide such as Ta, Zr, Ti, Si, Al, Nb, La, or a combination thereof can be used.

  In addition, after the oblique deposition film 13 is formed, annealing is performed to remove the color and to evaporate the moisture adsorbed between the columnar structures. The annealing treatment is preferably performed at 100 ° C. or higher at which water between the columnar structures is sufficiently evaporated. Further, if the temperature is raised too much, columnar structures grow and voids decrease, resulting in a decrease in birefringence, a decrease in transmittance, and the like. Further, after annealing, in order to prevent moisture in the atmosphere from entering and exiting the obliquely deposited film 13, a highly dense dielectric is formed by plasma CVD.

  In step S3, for the purpose of improving the transmittance, an antireflection film (AR film) is formed on both the front and back surfaces by sputtering. The AR film may be a multi-layered thin film composed of a generally used high refractive film and low refractive film.

  In step S4, it cuts into a desired size. For the cutting, a cutting device such as a glass scriber can be used.

  According to the above manufacturing method, a retardation element with reduced reflection of incident light and improved viewing angle dependency can be obtained.

<3. Application example to LCD projector>
Next, an application example will be described in which the retardation element according to the present embodiment functions as a quarter-wave plate and is mounted on a reflective liquid crystal projector using a reflective liquid crystal cell. In a reflective liquid crystal projector, plane polarized light is incident on an image displayed on a liquid crystal cell, predetermined plane polarized light is extracted from elliptically polarized light reflected by pixels corresponding to the image on the cell, and is projected on a screen by a projection lens. Projected on.

  FIG. 3 is a schematic cross-sectional view showing a configuration of a part of an optical engine used in a reflective liquid crystal projector. This reflective liquid crystal projector includes a polarizing beam splitter 21, a quarter-wave plate 22 to which the present technology is applied, and a liquid crystal cell 23.

  In this reflection type liquid crystal projector, the light emitted from the light source is converted into plane polarized light, then decomposed into R (red), G (green), and B (blue) color lights, and a polarized beam provided for each color. The light enters the splitter 21. S-polarized light reflected by the polarization plane of the polarizing beam splitter 21 or transmitted P-polarized light enters the reflective liquid crystal cell 23, and reflected light modulated for each pixel is emitted and returns to the polarizing beam splitter 21 again. At this time, the light incident on each polarization beam splitter 21 is not only parallel light but also light incident at a certain angle. Thereby, when the angle formed between the light beam incident on the polarization beam splitter 21 and the incident optical axis is increased, the contrast of the projected image is lowered. Therefore, a quarter wavelength plate 22 is disposed between the polarizing beam splitter 21 and the liquid crystal cell 23.

  Here, if incident light (here, S-polarized light) is slightly reflected at the substrate / vapor deposition film interface of the quarter-wave plate 22, the incident light travels back and forth through the quarter-wave plate. Under the same influence as when passing through the half-wave plate, it is converted from S-polarized light to P-polarized light. In this case, when it is desired to display the projection image in black with the reflective liquid crystal projector, the P-polarized light returns to the polarization beam splitter and is projected as a bright portion (white display), and the contrast of the projection image is greatly reduced.

  On the other hand, in the quarter-wave plate 22 to which the present technology is applied, since the reflection of incident light is reduced, all the light returning from the liquid crystal cell 23 to the polarization beam splitter 21 is S-polarized light, and the polarization beam splitter 22 is converted to P-polarized light. Therefore, the contrast of the projected image can be greatly improved.

  In a reflection type liquid crystal projector, the light incident on the quarter-wave plate 22 and the liquid crystal cell 23 generally has an angle dependency of about ± 10 degrees. Since the / 4 wavelength plate 22 has an angle dependency of the phase difference with respect to the incident light being small and symmetrical with respect to the normal incident light, the brightness and contrast can be improved.

  Note that the phase difference element to which the present technology is applied is not limited to the application example described above, and can be applied to an optical apparatus such as an optical pickup or a laser apparatus, for example.

<4. Example>
Examples of the present invention will be described below, but the present invention is not limited to these examples.

<4.1 Simulation for forming interface antireflection film of retardation element>
A simulation was performed to form an interface antireflection film for a quarter-wave plate. Here, first, the phase difference element in which the interface antireflection film is not formed and the phase difference element in which the interface antireflection film is formed are compared. Then, a three-layer structure in which a high refractive index film and a low refractive index film are alternately stacked was examined as an interface antireflection film capable of reducing the reflectance.

[Phase difference element in which no interface antireflection film is formed]
FIG. 4 is a schematic diagram showing a simulation model of a retardation element in which no interface antireflection film is formed. In this retardation element, the transparent substrate was made of quartz, and the obliquely deposited film was made of Ta 2 O 5. Further, an antireflection film (AR) was provided only on the surface.

FIG. 5 is a graph showing the refractive index wavelength dispersion of the quartz substrate and the Ta ₂ O ₅ oblique deposition film. FIG. 6 is a graph showing the reflectance of the retardation element in which the interface antireflection film is not formed.

  As can be seen from FIGS. 5 and 6, there is a large refractive index difference between the quartz substrate and the obliquely deposited film. In the structure of the phase difference element shown in FIG. 4, the reflectances of both the s-polarized component and the p-polarized component ( It has been found that it is difficult to reduce (Rp, Rs).

[Phase difference element with interface antireflection film]
Next, a simulation was performed on a retardation element in which an interface antireflection film was formed between a transparent substrate and an oblique deposition film. As shown in FIG. 7, the phase difference element was formed with an interface antireflection film between the transparent substrate and the oblique deposition film. Other than that, like the retardation element shown in FIG. 4, the transparent substrate 11 was made of quartz, and the oblique deposition film 13 was made of Ta ₂ O ₅ . Further, an antireflection film (AR) was provided only on the surface.

FIG. 8 is a graph showing the refractive index wavelength dispersion of the Al ₂ O ₃ interface antireflection film, the quartz substrate, and the Ta ₂ O ₅ oblique deposition film. FIG. 9 is a graph showing the reflectance of the retardation element on which the Al ₂ O ₃ interface antireflection film is formed.

As can be seen from FIGS. 8 and 9, the Al ₂ O ₃ interface antireflection film has a higher refractive index than the Ta ₂ O ₅ oblique deposition film, and the effect of reducing the reflectance (Rp, Rs) in the blue wavelength band. Was found to be small.

FIG. 10 is a graph showing the refractive index wavelength dispersion of the SiO 2 interface antireflection film, the quartz substrate, and the Ta ₂ O ₅ oblique deposition film. FIG. 11 is a graph showing the reflectance of the retardation element on which the SiO ₂ interface antireflection film is formed.

As can be seen from FIGS. 10 and 11, the SiO ₂ interface antireflection film has a small difference in refractive index from that of the quartz substrate, and it has been found that the effect of reducing the reflectance (Rp, Rs) in the blue wavelength band is small.

  Next, the refractive index of the optimum interface antireflection film that reduces the reflectivity of the retardation element was determined by simulation.

FIG. 12 is a graph showing the refractive index wavelength dispersion of the optimum interface antireflection film, the quartz substrate, and the Ta ₂ O ₅ oblique deposition film. FIG. 13 is a graph showing the reflectance of the retardation element on which the optimum interface antireflection film is formed.

As can be seen from FIGS. 12 and 13, the refractive index of the optimum interface antireflection film is higher than that of the quartz substrate and lower than that of the Ta ₂ O ₅ oblique deposition film. It has been found that this optimum interface antireflection film has a great effect of reducing the reflectance (Rp, Rs), and a reflectance (Rp, Rs) of 0.2% or less can be obtained in the blue wavelength band.

  From the above, it is possible to reduce the reflectance of the retardation element by making the refractive index of the interface antireflection film higher than the refractive index of the transparent substrate and smaller than the refractive index of the oblique deposition film. I understood.

[Three-layer structure interface antireflection film]
Since the above-mentioned optimum interface antireflection film does not have a material satisfying the optimum refractive index with a single layer, the optimum interface antireflection film by lamination was simulated. As a result, a single-layer optimum interface antireflection film having an optimum design film thickness of 66 nm can be realized by a three-layer structure film in which an SiO ₂ film, an Nb ₂ O ₅ film, and an SiO ₂ film are laminated in this order. I understood.

FIG. 14 is a graph showing the reflectance of the optimum interface antireflection film. FIG. 15 is a graph showing the reflectivity of the three-layer structure film and the optimum interface antireflection film. From the graph shown in FIG. 15, by laminating the SiO2 film to 76 nm, the Nb ₂ O ₅ film to 3.3 nm, and the SiO2 film to 44 nm in this order, the reflectivity is almost equal to the optimum reflectivity of the optimum interface antireflection film. It turns out that they match.

FIG. 16 is a graph showing the reflectance when the thickness of the Nb ₂ O ₅ film of the three-layer structure film is 2.3 nm, 3.3 nm, or 4.3 nm. From the graph shown in FIG. 16, Nb ₂ O ₅ when the thickness of the film changes ± 1 nm greatly reflectance is changed, the thickness of the Nb ₂ O ₅ film was found to be important.

FIG. 17 is a graph showing the reflectance of the retardation element when the second layer having the three-layer structure is an Al ₂ O ₃ film. Although optimization was attempted by replacing the Nb ₂ O ₅ film having a three-layer structure with an Al ₂ O ₃ film, for example, as shown in FIG. 17, since the refractive index of the Al ₂ O ₃ film is relatively small, the blue wavelength It was found that the effect of reducing the reflectance (Rp, Rs) was small in the band.

FIG. 18 is a graph showing the reflectance of the retardation element when the second layer having the three-layer structure is an Nb ₂ O ₅ film. When the SiO ₂ film was optimized to 95 nm, the Nb ₂ O ₅ film was optimized to 3.0 nm, and the SiO ₂ film was optimized to 35 nm, a reflectance (Rp, Rs) of 0.2% or less was obtained in the blue wavelength band.

Further, from the results shown in FIGS. 17 and 18, it was found that the second layer having the three-layer structure can be substituted with a high refractive material such as TiO ₂ , LaTiO ₃ , Ta ₂ O ₅ .

  FIG. 19 is a graph showing the reflectivity of a retardation element having a three-layer interface antireflection film and a retardation element having no interface antireflection film. As apparent from the graph shown in FIG. 19, by providing an interface antireflection film in which a high refractive index film and a low refractive index film are alternately laminated between a transparent substrate and an oblique deposition film, a phase difference is obtained. It was found that the reflectance (Rp, Rs) of the element can be reduced.

[Relationship between oblique deposition film and interface antireflection film]
Next, simulation was performed on the relationship between the refractive index of the oblique deposition film and the three-layer interface antireflection film in which the SiO ₂ film, the Nb ₂ O ₅ film, and the SiO ₂ film were laminated in this order. The refractive index of the transparent substrate at a wavelength of 450 nm was 1.47.

FIG. 20 is a graph showing the reflectance of the retardation element in which the three-layer structure antireflection film is formed with respect to the refractive index of the oblique deposition film. Here, the interface antireflection film has a three-layer structure in which the SiO ₂ film is 93 nm, the Nb ₂ O ₅ film is 3 nm, and the SiO ₂ film is 35 nm in this order.

From the graph shown in FIG. 20, the refractive indexes n _oblx and n _obly (n _oblx > n _obly ) of the in-plane orthogonal two axes x and y of the oblique deposition film are in the range of 1.55 or more and 1.7 or less. It was found that the reflectance in the blue wavelength band (440 to 510 nm) was 0.3% or less.

Table 1 shows the simulation results of the effective film thickness range of the Nb ₂ O ₅ film with respect to the refractive indexes n _oblx , n _obly (n _oblx > n _obly ) of the oblique deposition film.

When the refractive index n _oblx , n _obly (n _oblx > n _obly ) of the oblique deposition film is 1.55, the effective film thickness range of the Nb ₂ O ₅ film is 0.5 to 3.5 nm. It was found that the effective film thickness range of the Nb ₂ O ₅ film is 3.0 to 5.5 nm when the refractive indexes _nob1x and _nobly ( _nob1x > _nobly ) are 1.70.

Next, as shown in FIG. 21, the Nb ₂ O ₅ film of the second layer having the three-layer structure is fixed to 3 nm, and the thicknesses of the SiO ₂ film of the first layer and the SiO ₂ film of the third layer are changed. A simulation was performed. From the graph shown in FIG. 21, it was found that the reflectivity did not vary greatly even when the thicknesses of the first layer SiO ₂ film and the third layer SiO ₂ film varied by ± 10 nm.

From these simulation results, the interface antireflection film having the three-layer structure in which the low refractive index film, the high refractive index film, and the low refractive index film are laminated in this order has a refractive index n _L of the low refractive index film of 1.5. It has been found that the reflectance can be reduced when the refractive index n _H of the high refractive index film is smaller than 2.0. _Each of the refractive indexes n _oblx and n _obly (n _oblx > n _obly ) of the in-plane orthogonal two axes x and y of the oblique vapor deposition film is in the range of 1.55 to 1.7 and has a three-layer structure. It has been found that when the film thickness of the high refractive index film is in the range of 0.1 to 5.5 nm, a reflectance of 0.3% or less can be realized in the blue wavelength band (440 to 510 nm).

<4.2 Production of 1/4 wavelength plate>
Next, in order to verify the above-mentioned simulation result, a quarter wavelength plate was produced. FIG. 22 is a schematic diagram illustrating the structure of the retardation element of the example. FIG. 23 is a schematic diagram showing the structure of a retardation element of a comparative example.

[Example]
On the quartz substrate, a dielectric film (interface antireflection film) having an intermediate value between the refractive index of the quartz substrate and the refractive index of the obliquely deposited film was formed by sputtering. The interface antireflection film has a structure in which two types of materials, a relatively high refractive index material and a low refractive index material, are alternately stacked. Specifically, the structure is quartz substrate / SiO ₂ (93 m) / Nb ₂ O ₅ (3 nm) / SiO ₂ (35 nm), and the optical properties of the oblique deposition film do not vary at the top of the interface antireflection film. Thus, the same material as the substrate was SiO ₂ .

Next, we deposited deposition material mainly composed of Ta ₂ O ₅ as the vapor deposition source with respect to the normal direction of the quartz substrate is 70 °. At this time, each time the film was formed to 7 nm, the quartz substrate was rotated 180 ° in the in-plane direction to produce an oblique vapor deposition film composed of multiple layers having different film forming directions. The thickness of all layers of the oblique vapor deposition film was about 900 nm which functions as a quarter wavelength plate in the blue wavelength band.

[Comparative example]
A retardation element of a comparative example was produced in the same manner as in the example, except that a two-layer oblique vapor deposition film was produced on a quartz substrate without forming an interface antireflection film.

A vapor deposition material mainly composed of Ta ₂ O ₅ was deposited on a quartz substrate so that the vapor deposition source was 70 ° with respect to the normal direction of the substrate. At this time, after forming the film at 750 nm, the substrate was rotated 180 ° to prepare an oblique vapor deposition film composed of two layers having different film forming directions. The thickness of the two layers was about 1500 nm, which functions as a quarter wavelength plate in the blue wavelength band. As described above, the retardation element of the comparative example shown in FIG. 23 was produced.

[Optical Properties of Examples and Comparative Examples]
FIG. 24 is a graph showing the wavelength dependence of retardation (Re). It was confirmed that the retardation elements of Examples and Comparative Examples had a retardation of 460 nm of about 115 nm and functioned as a quarter wavelength plate.

  FIG. 25 is a graph showing the wavelength dependence of transmittance. FIG. 26 is a graph showing the wavelength dependence of reflectance. It was found that the retardation element of the example had a transmittance about 1% higher and a reflectance about 0.5% lower than the retardation element of the comparative example. The decrease in reflectance is an effect of multilayering of the interface antireflection film and the oblique deposition film, and the transmittance can also be improved by reducing the reflectance.

Next, a simulation was performed to estimate the effect of the interface antireflection film. For the retardation element produced in the example, the reflectance in the blue wavelength band is calculated for the presence or absence of an interface antireflection film having a three-layer structure of SiO ₂ (93 m) / Nb ₂ O ₅ (3 nm) / SiO ₂ (35 nm). did.

  FIG. 27 is a graph showing the reflectivity of the retardation elements of the example and the comparative example. Compared to the retardation element of the comparative example without the interface antireflection film, the retardation element of the example with the interface antireflection film showed an effect of halving both the average value and the peak value of the reflectance.

  In addition to the reduction in reflectance, the present technology has been found to have an effect of improving the viewing angle dependency. FIG. 28 and FIG. 29 are graphs showing the incident angle dependence of the retardation of the retardation element of the example. FIG. 30 is a graph showing the incident angle dependency of retardation of the retardation element of the comparative example.

  As shown in FIG. 31, in the phase difference element plane, the fast axis (direction parallel to the oblique deposition direction) is the x axis, the slow axis (direction perpendicular to the oblique deposition direction) is the y axis, and the element. The incident light angle from the z-axis direction was set to 0 when the normal direction was the z-axis. In addition, an angle when the incident light is tilted on the xz plane is θ, and an angle when the incident light is tilted on the yz plane is φ. The graphs shown in FIGS. 28 to 30 are normalized by the retardation value when the incident light angle is zero.

  It was found that the retardation element of the example has a symmetrical distribution of retardation with respect to the optical axis. In the retardation element of the comparative example, the retardation in the θ direction is relatively bilaterally symmetric, but the retardation in the φ direction could not be accurately measured. The reason is that when the oblique vapor deposition film is laminated with a film thickness that is not sufficiently smaller than the wavelength of light as in the comparative example, it is considered that two phase difference elements having different birefringence axes are overlapped, This is because a simple evaluation of “refractive index difference and axial direction” cannot be performed. Therefore, it is difficult to use the phase difference element of the comparative example with respect to incident light having angle dependency.

  Since the phase difference element of the example is laminated with a film thickness sufficiently smaller than the wavelength of light, the birefringence axis of each layer can be ignored, and one axis in all layers (in the case of the example, z Since it can be regarded as a phase difference element having an axial direction), it has been found that it can be an appropriate phase difference element for incident light having angle dependency.

  As described above, by introducing an interface antireflection film and further reducing the film thickness per layer of the obliquely deposited film to the working wavelength or less, the reflectance is reduced and the angle dependency is improved symmetrically. I found out.

  When the phase difference elements of these examples and comparative examples are applied to a reflective liquid crystal projector as a quarter wavelength plate for a blue wavelength band, the phase difference elements of the comparative examples are applied when the phase difference elements of the examples are applied. Compared to the case of applying, improvement of 1% in brightness and 5% in contrast was observed. Naturally, further improvement in brightness and contrast can be expected by applying the present technology as a quarter wavelength plate for green wavelength band and red.

  In addition, this invention is not limited to these Examples, Of course, a various deformation | transformation and change can be performed in the range which does not deviate from the meaning of this invention. For example, in the retardation element of the above-described embodiment, since the thickness of each layer is equal, the birefringence axis is in the z-axis direction. For example, the axial direction can be arbitrarily tilted by changing the thickness of each layer. It may be.

  In the above-described embodiments, the quarter wavelength plate of the blue wavelength band has been described. However, the present technology can be applied to the quarter wavelength plate of the green wavelength band, the red wavelength band, the half wavelength plate of each channel, and the broadband. The present invention may be applied to a quarter wavelength plate, a half wavelength plate, a phase difference compensation element, and the like.

  DESCRIPTION OF SYMBOLS 11 Transparent substrate, 12 Interface antireflection film, 13 Orthorhombic vapor deposition film, 14 CVD dielectric film, 15A, 15B Antireflection film, 21 Polarization beam splitter, 22 1/4 wavelength plate, 23 Liquid crystal cell

Claims (11)

A transparent substrate;
Diagonal vapor deposition films in which dielectric materials are alternately obliquely deposited from two directions different from each other by 180 °, and the thickness of each layer is equal to or less than a use wavelength;
It consists of three dielectric layers in which a high refractive index film is sandwiched between two low refractive index films between the transparent substrate and the oblique vapor deposition film, and the refractive index of the low refractive index film is smaller than 1.5. An interface antireflection film having a refractive index of the high refractive index film of greater than 2.0 and a film thickness of the high refractive index film of 0.5 nm to 5 nm;
The average refractive index of the interface antireflection film composed of the three dielectric layers is larger than the refractive index of the transparent substrate, and smaller than the refractive index of the oblique deposition film,
A phase difference element having a refractive index in two directions of the oblique vapor deposition film in a range larger than 1.55 and smaller than 1.7. 2. The phase difference element according to claim 1, wherein an average refractive index n of the interface antireflection film has a relationship represented by the following formula (1).
Here, nsub is the refractive index of the transparent _{substrate, n oblx, n obly (n} oblx> n obl y) is the two orthogonal axes x, the refractive index of y of each of the oblique deposition film plane. The phase difference element according to claim 1, wherein the interface antireflection film is made of SiO ₂ in contact with the oblique deposition film.   The phase difference element according to claim 1, wherein the thickness of the interface antireflection film is 90% or less of the design center wavelength. The retardation element according to claim 3, wherein a film thickness of SiO ₂ in contact with the oblique deposition film is 60 nm or more.   The retardation element according to claim 1, further comprising a CVD (Chemical Vapor Deposition) film made of a dielectric material on the oblique vapor deposition film.   The phase difference element of any one of Claims 1 thru | or 6 provided with an anti-reflective film on both front and back.   The dielectric material of the oblique deposition film is an oxide of Ta, Zr, Ti, Si, Al, Nb, or La, or a combination thereof. Phase difference element. It consists of three dielectric layers in which a low refractive index film and a high refractive index film are alternately laminated on a transparent substrate, and the high refractive index film is sandwiched between two low refractive index films. The average refractive index of the transparent substrate is larger than the refractive index of the transparent substrate, smaller than the refractive index of the oblique deposition film to be formed next, the refractive index of the low refractive index film is smaller than 1.5, and the high refractive index film Forming an interface antireflection film having a refractive index greater than 2.0 and a high refractive index film thickness of 0.5 nm to 5 nm,
Dielectric materials are alternately obliquely deposited from two directions different from each other by 180 ° on the interface antireflection film, and the refractive indexes in the two directions are in the range of more than 1.55 and less than 1.7. A method of manufacturing a phase difference element, wherein an obliquely deposited film having a thickness equal to or less than a working wavelength is formed. Between the transparent substrate, the dielectric material is alternately obliquely deposited from two directions different from each other by 180 °, and the thickness of each layer is equal to or less than the use wavelength, and between the transparent substrate and the obliquely deposited film, 2 It consists of three dielectric layers with a high refractive index film sandwiched between one sheet of low refractive index film. The refractive index of the low refractive index film is smaller than 1.5 and the refractive index of the high refractive index film is larger than 2.0. A high refractive index film having an interface antireflection film having a film thickness of 0.5 nm to 5 nm , and an average refractive index of the interface antireflection film composed of the three dielectric layers is larger than the refractive index of the transparent substrate, A phase difference element having a refractive index smaller than the refractive index of the oblique deposition film and having a refractive index in two directions of the oblique deposition film larger than 1.55 and smaller than 1.7 is different from each other. A liquid crystal projector placed between the liquid crystal cells.   Between the transparent substrate, the dielectric material is alternately obliquely deposited from two directions different from each other by 180 °, and the thickness of each layer is equal to or less than the use wavelength, and between the transparent substrate and the obliquely deposited film, 2 It consists of three dielectric layers with a high refractive index film sandwiched between one sheet of low refractive index film. The refractive index of the low refractive index film is smaller than 1.5 and the refractive index of the high refractive index film is larger than 2.0. A high refractive index film having an interface antireflection film having a film thickness of 0.5 nm to 5 nm, and an average refractive index of the interface antireflection film composed of the three dielectric layers is larger than the refractive index of the transparent substrate, An optical system in which different phase difference elements are mounted in which the refractive index in the two directions of the oblique vapor deposition film is smaller than the refractive index of the oblique vapor deposition film and is larger than 1.55 and smaller than 1.7. machine.