JP2018109754A - Polarizing plate, method for producing the same, and optical instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate having high transmittance characteristics and excellent control of reflectance characteristics, a method for manufacturing the same, and an optical device provided with the polarizing plate. SOLUTION: The polarizing plate 1 has a wire grid structure, and is arranged on the transparent substrate 10 at a pitch shorter than the wavelength of light in the used band and extends in a predetermined direction. 11. The lattice-shaped convex portion 11 has a pedestal 12, a reflective layer 13, a dielectric layer 14, and an absorbing layer 15 in this order from the transparent substrate 10 side, and the pedestal 12 has a lattice-like shape. It has a trapezoidal shape when viewed from the extending direction of the convex portion 11. [Selection diagram] Fig. 1

Description

  The present invention relates to a polarizing plate, a manufacturing method thereof, and an optical apparatus.

  Conventionally, in a wire grid type polarizing plate, the light transmittance decreases in principle on the shorter wavelength side from the relationship between the pitch according to the wavelength of light in the use band and the grid width (width in the grid arrangement direction). It is known. In particular, in the visible light region (red band: wavelength λ = 600 to 680 nm, green band: wavelength λ = 520 to 590 nm, blue band: wavelength λ = 430 to 510 nm) used in a liquid crystal projector, the blue band has the highest transmittance. Becomes lower.

  On the other hand, it is known that the transmittance can be increased by narrowing the grid width of the polarizing plate. However, it is difficult to form a pattern in which the grid width is actually narrowed from the viewpoint of increasing manufacturing variation, and it is difficult to maintain the reliability as a polarizing plate.

  Therefore, the applicant of the present invention is a wire grid type having a plurality of linear metal layers, a plurality of linear dielectric layers, and a plurality of linear light absorption layers having a light absorption function on a transparent substrate in this order. In the inorganic polarizing plate, the cross-sectional shape of the linear metal layer in the cross section orthogonal to the longitudinal direction of the linear metal layer is a trapezoidal shape with the substrate side as the bottom and the linear dielectric layer side as the bottom. An inorganic polarizing plate in which the bottom length is longer than the length of the upper bottom has been proposed (see, for example, Patent Document 1). According to the inorganic polarizing plate of Patent Document 1, excellent polarization characteristics can be obtained by the cross-sectional shape of the linear metal layer.

JP2016-45345A

  However, in recent years, there has been a demand for a polarizing plate having higher transmittance characteristics and excellent control of reflectance characteristics. The present invention has been made in view of the above, and an object of the present invention is to provide a polarizing plate having high transmittance characteristics and excellent control of reflectance characteristics, a manufacturing method thereof, and an optical apparatus including the polarizing plate. There is.

  In order to achieve the above object, the present invention provides a polarizing plate having a wire grid structure, on a transparent substrate (for example, transparent substrate 10 described later) and a pitch shorter than the wavelength of light in the use band on the transparent substrate. A grid-like convex part (for example, a grid-like convex part 11 described later) that is arranged and extends in a predetermined direction, and the grid-shaped convex part is arranged in order from the transparent substrate side (for example, a base that is described later). 12), a reflective layer (for example, a later-described reflective layer 13), a dielectric layer (for example, a later-described dielectric layer 14), and an absorbing layer (for example, an after-mentioned absorbing layer 15), A pedestal provides a polarizing plate (for example, a polarizing plate 1 described later) having a trapezoidal shape when viewed from the predetermined direction.

  The minimum width of the pedestal may be equal to or greater than the width of the reflective layer (for example, the width c of the reflective layer described later).

  The said base may be comprised with the Si oxide transparent with respect to the wavelength of the light of a use zone | band.

  A tapered shape with a side surface inclined in a direction in which the width of the grid front end portion (for example, grid front end portion 17 to be described later) formed at the front end of the lattice-shaped convex portion becomes narrower toward the front end side when viewed from the predetermined direction. You may have.

  The grid tip is composed of the dielectric layer and the absorbing layer, the maximum width of the grid tip (for example, grid width b described later) is 35 to 45 nm, and the width of the reflective layer is It may be 52 to 72% with respect to the maximum width of the grid tip.

The inclination angle of the side surface of the grid tip with respect to the transparent substrate is θ, the height of the grid tip when viewed from the predetermined direction is a, the maximum width of the grid tip is b, θ ₀ = arctan ( 2a / b), 2/3 ≦ a / b ≦ 8/7 is satisfied, θ ₀ ≦ θ <90 degrees is satisfied, and the inclination angle θ absorbs light having a predetermined wavelength in the visible light region. You may select from the angle range which makes the reflectance of an axial direction 10% or less.

  The inclination angle θ is defined as an inclination angle of a tangent to the side surface of the grid tip at the center position in the height direction of the grid tip when viewed from the predetermined direction, and the angle range is θ ≦ 80. May be degrees.

  The transparent substrate may be transparent to the wavelength of light in the use band, and may be made of glass, crystal, or sapphire.

  The reflective layer may be made of aluminum or an aluminum alloy.

  The dielectric layer may be made of Si oxide.

  The absorption layer may include Fe or Ta and Si.

  The surface of the polarizing plate on which light is incident may be covered with a protective film made of a dielectric.

  The surface of the polarizing plate on which light is incident may be covered with an organic water-repellent film.

  Further, the present invention is a method for manufacturing a polarizing plate having a wire grid structure, wherein a base layer forming step of forming a base layer on a transparent substrate, and a reflective layer forming step of forming a reflective layer on the base layer, A dielectric layer forming step of forming a dielectric layer on the reflective layer; an absorption layer forming step of forming an absorption layer on the dielectric layer; and selectively etching the formed laminate. An etching step of forming a grid-like convex portion arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use band, and in the etching step, the grid layer is etched by etching the base layer. Provided is a method for producing a polarizing plate that forms a pedestal having a trapezoidal shape when viewed from the extending direction of a convex portion.

  In addition, the present invention provides an optical device including the polarizing plate.

  ADVANTAGE OF THE INVENTION According to this invention, the polarizing plate which was excellent in control of the reflectance characteristic while having a high transmittance | permeability characteristic, its manufacturing method, and an optical apparatus provided with the polarizing plate can be provided.

It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram for demonstrating the shape parameter of the polarizing plate which concerns on the said embodiment. It is a cross-sectional schematic diagram for demonstrating the inclination | tilt angle of the grid front-end | tip part of the polarizing plate which concerns on the said embodiment. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on the modification 1 of the said embodiment. It is a graph which shows the result of having verified by transmission the transmission axis transmittance Tp of the polarizing plate of the structure shown in FIG. 1, and the polarizing plate of the structure shown in FIG. It is a graph which shows the result of having verified by the simulation the relationship between the width | variety of the reflection layer of the polarizing plate of the structure shown in FIG. 1, and the transmission axis transmittance | permeability Tp. It is a graph which shows the result of having verified by simulation the relationship between the width | variety of the reflection layer of the polarizing plate of the structure shown in FIG. 1, and contrast CR. It is a cross-sectional schematic diagram which shows the polarizing plate which does not have a base. It is a graph which shows the result of having verified by transmission the transmission axis transmittance Tp of the polarizing plate of the structure shown in FIG. 4, and the polarizing plate of the structure shown in FIG. It is a cross-sectional schematic diagram which shows the polarizing plate whose grid front-end | tip part is a rectangular shape. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the transmission axis transmittance Tp when the ratio of the height a of the grid tip to the grid width b is a: b = 6: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the absorption axis reflectance Rs when the ratio of the height a of the grid tip to the grid width b is a: b = 6: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the transmission axis transmittance Tp when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 11. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the absorption axis reflectance Rs when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 11. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the transmission axis transmittance Tp when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the absorption axis reflectance Rs when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the transmission axis transmittance Tp when the ratio of the height a of the grid tip to the grid width b is a: b = 10: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the absorption axis reflectance Rs when the ratio of the height a of the grid tip to the grid width b is a: b = 10: 9. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the transmission axis transmittance Tp when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 7. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the relationship between the inclination angle θ of the grid tip and the absorption axis reflectance Rs when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 7. It is a graph which shows the result of having verified by simulation. In the polarizing plate having the structure shown in FIG. 1, the measured value of the transmission axis transmittance Tp with respect to the inclination angle θ of the side surface of the grid front end when the ratio of the height a of the grid front end to the grid width b is 8: 9. It is a graph which shows the result verified by comparing with a simulation result. 2 is a graph showing measured values of transmission axis transmittance Tp when the grid inclination angle θ is different in the polarizing plate having the structure shown in FIG. 1. 2 is a graph showing measured values of absorption axis transmittance Ts when the grid inclination angle θ is different in the polarizing plate having the structure shown in FIG. 1. 2 is a graph showing measured values of transmission axis reflectivity Rp when the grid inclination angle θ is different in the polarizing plate having the structure shown in FIG. 1. 2 is a graph showing measured values of absorption axis reflectivity Rs when the grid inclination angle θ is different in the polarizing plate having the structure shown in FIG. 1.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Polarizer]
A polarizing plate according to an embodiment of the present invention is an inorganic polarizing plate having a wire grid structure, and is arranged on a transparent substrate at a pitch (period) shorter than the wavelength of light in a use band and is predetermined on the transparent substrate. A grid-like convex portion extending in the direction. Moreover, this lattice-shaped convex part has a base, a reflection layer, a dielectric material layer, and an absorption layer in order from the transparent substrate side.

  FIG. 1 is a schematic cross-sectional view showing a polarizing plate 1 according to an embodiment of the present invention. As shown in FIG. 1, the polarizing plate 1 includes a transparent substrate 10 that is transparent to light in the use band, and a lattice-like protrusion arranged on one surface of the transparent substrate 10 at a pitch shorter than the wavelength of the light in the use band. Unit 11. The lattice-shaped convex portion 11 includes a pedestal 12, a reflective layer 13, a dielectric layer 14, and an absorption layer 15 in order from the transparent substrate 10 side. That is, the polarizing plate 1 has a grid-like convex portion 11 formed by laminating a pedestal 12, a reflective layer 13, a dielectric layer 14 and an absorption layer 15 in this order from the transparent substrate 10 side. It has a wire grid structure arranged in a grid.

  Here, as shown in FIG. 1, the extending direction (predetermined direction) of the grid-like convex portions 11 is referred to as a Y-axis direction. A direction perpendicular to the Y-axis direction and in which the grid-like convex portions 11 are arranged along the main surface of the transparent substrate 10 is referred to as an X-axis direction. In this case, the light incident on the polarizing plate 1 is preferably incident from the direction orthogonal to the X-axis direction and the Y-axis direction on the side of the transparent substrate 10 on which the grid-like convex portions 11 are formed.

  The polarizing plate 1 utilizes four actions of selective light absorption of a polarized wave due to transmission, reflection, interference, and optical anisotropy, thereby causing a polarized wave (TE wave (S wave (S) (S wave (S)) to be parallel to the Y-axis direction. Wave)) is attenuated, and a polarized wave (TM wave (P wave)) having an electric field component parallel to the X-axis direction is transmitted. Accordingly, the Y-axis direction is the direction of the absorption axis of the polarizing plate 1, and the X-axis direction is the direction of the transmission axis of the polarizing plate 1.

  A part of the light incident from the side of the polarizing plate 1 on which the lattice-shaped convex portions 11 are formed passes through the absorption layer 15 and the dielectric layer 14 and is attenuated. Of the light transmitted through the absorption layer 15 and the dielectric layer 14, the polarized wave (TM wave (P wave)) is transmitted through the reflective layer 13 with high transmittance. On the other hand, of the light transmitted through the absorption layer 15 and the dielectric layer 14, the polarization wave (TE wave (S wave)) is reflected by the reflection layer 13. The TE wave reflected by the reflection layer 13 is partially absorbed when passing through the absorption layer 15 and the dielectric layer 14, and part of the TE wave is reflected back to the reflection layer 13. Further, the TE wave reflected by the reflection layer 13 is attenuated by interference when passing through the absorption layer 15 and the dielectric layer 14. As described above, the polarizing plate 1 can obtain desired polarization characteristics by selectively attenuating the TE wave.

As shown in FIG. 1, the grid-shaped convex portions 11 are formed in a trapezoidal pedestal 12 and a rectangular shape when viewed from the extending direction (predetermined direction) of each one-dimensional grid, that is, in a cross-sectional view orthogonal to the predetermined direction. Grid leg portion 16 and a tapered grid tip portion 17.
The grid legs 16 are formed to extend vertically from the base 12. The grid leg 16 is composed of the reflective layer 13. That is, the boundary between the grid leg 16 and the grid tip 17 is located at the boundary between the reflective layer 13 and the dielectric layer 14.
The grid front end portion 17 has a tapered shape whose side surface is inclined in a direction in which the width becomes narrower toward the front end side (opposite side of the transparent substrate 10) when viewed from a predetermined direction. In more detail, the grid front-end | tip part 17 of this embodiment has an isosceles trapezoid shape. The grid tip 17 is composed of a dielectric layer 14 and an absorption layer 15.

  By making the grid tip 17 tapered, the TM wave transmittance can be increased. The reason why the transmittance of the TM wave is increased in this way is considered to be that the grid tip 17 has a tapered shape, and thus has an effect of suppressing scattering with respect to light incident with an angular variation. .

  Here, FIG. 2 is a schematic cross-sectional view for explaining the shape parameters of the polarizing plate 1 according to this embodiment. In the following description, the height means a dimension in a direction perpendicular to the main surface of the transparent substrate 10, and the width means the height when viewed from the Y-axis direction along the extending direction of the lattice-shaped convex portions 11. It means the dimension in the X-axis direction orthogonal to the direction. Further, when the polarizing plate 1 is viewed from the Y-axis direction along the direction in which the lattice-shaped convex portions 11 extend, the repetition interval in the X-axis direction of the lattice-shaped convex portions 11 is referred to as a pitch P.

  The pitch P of the grid-like convex portions 11 is not particularly limited as long as it is shorter than the wavelength of light in the use band. From the viewpoint of ease of manufacture and stability, the pitch P of the lattice-shaped convex portions 11 is preferably, for example, 100 nm to 200 nm. The pitch P of the grid-like convex portions 11 can be measured by observing with a scanning electron microscope or a transmission electron microscope. For example, the pitch P can be measured at any four locations using a scanning electron microscope or a transmission electron microscope, and the arithmetic average value can be used as the pitch P of the lattice-shaped convex portions 11. Hereinafter, this measurement method is referred to as electron microscopy.

  Further, the maximum width in the X-axis direction at the grid front end portion 17 of the grid-like convex portion 11 is referred to as a grid width b. In the present embodiment, the grid width b means the width of the end portion on the reflective layer 13 side in the grid front end portion 17. Specifically, the grid width b is preferably 35 to 45 nm. Note that these widths can be measured by, for example, the electron microscopy described above.

  In addition, an inclination angle of the side surface of the grid tip portion 17 with respect to the transparent substrate 10 is referred to as an inclination angle θ, and a height of the grid tip portion 17 is referred to as a height a. However, since the grid-like convex part 11 has a very fine structure, the shape of the grid tip part 17 is actually rounded to some extent as shown in FIG. 3, for example. Therefore, the inclination angle θ is defined as the inclination angle with respect to the transparent substrate 10 of the side surface of the grid front end portion 17 at the center position of the height a of the grid front end portion 17, that is, the position of height a / 2. At this time, a specific range of the inclination angle θ is preferably θ ≦ 80 degrees. Note that the inclination angle θ and the height a can be measured by, for example, the above-described electron microscopy.

When θ ₀ = arctan (2a / b), the polarizing plate 1 according to the present embodiment satisfies 2/3 ≦ a / b ≦ 8/7 and satisfies θ ₀ ≦ θ <90 degrees. Is preferred. At this time, the inclination angle θ is preferably selected from an angle range in which the reflectance in the absorption axis direction of light having a predetermined wavelength in the visible light region is 10% or less.

  The transparent substrate 10 is not particularly limited as long as it is a substrate exhibiting translucency with respect to light in the use band, and can be appropriately selected according to the purpose. “Showing translucency with respect to the light in the use band” does not mean that the light transmittance in the use band is 100%, but the translucency capable of maintaining the function as a polarizing plate. Show it. Examples of the light in the use band include visible light having a wavelength of about 380 nm to 810 nm.

  The main surface shape of the transparent substrate 10 is not particularly limited, and a shape (for example, a rectangular shape) according to the purpose is appropriately selected. The average thickness of the transparent substrate 10 is preferably 0.3 mm to 1 mm, for example.

  The constituent material of the transparent substrate 10 is preferably a material having a refractive index of 1.1 to 2.2, and examples thereof include glass, crystal, and sapphire. From the viewpoint of cost and light transmittance, it is preferable to use glass, particularly quartz glass (refractive index 1.46) or soda lime glass (refractive index 1.51). The component composition of the glass material is not particularly limited, and for example, an inexpensive glass material such as silicate glass widely distributed as optical glass can be used.

  From the viewpoint of thermal conductivity, it is preferable to use quartz or sapphire having high thermal conductivity. Thereby, high light resistance with respect to strong light is obtained, and it is preferably used as a polarizing plate for an optical engine of a projector that generates a large amount of heat.

  When a transparent substrate made of an optically active crystal such as quartz is used, it is preferable to arrange the lattice-like convex portions 11 in a direction parallel to or perpendicular to the optical axis of the crystal. Thereby, excellent optical characteristics can be obtained. Here, the optical axis is a direction axis that minimizes the difference in refractive index between O (ordinary ray) and E (extraordinary ray) of light traveling in that direction.

  As shown in FIG. 1, the pedestal 12 has a trapezoidal shape when viewed from the extending direction (predetermined direction) of each one-dimensional lattice, that is, in a cross-sectional view orthogonal to the predetermined direction. More specifically, the pedestal 12 according to the present embodiment has an isosceles trapezoidal shape whose side surface is inclined so that the width decreases from the transparent substrate 10 side toward the reflective layer 13 side when viewed from a predetermined direction.

  The minimum width of the base 12 is preferably equal to or greater than the width of the reflective layer 13. That is, the width of the end portion on the reflective layer 13 side of the pedestal 12 having the narrowest width is equal to or larger than the width of the reflective layer 13. More preferably, the minimum width of the base 12 is set larger than the width of the reflective layer 13. Note that these widths can be measured by, for example, the electron microscopy described above.

  The film thickness of the pedestal 12 is not particularly limited, and is preferably 10 nm to 100 nm, for example. The film thickness of the pedestal 12 can be measured by, for example, the above-described electron microscopy.

The pedestal 12 is formed by arranging a dielectric film extending in a band shape in the Y-axis direction as an absorption axis on the transparent substrate 10. The constituent material of the pedestal 12 is preferably a material that is transparent to light in the use band and has a refractive index smaller than that of the transparent substrate 10, and among these, Si oxides such as SiO ₂ are preferable.

  The pedestal 12 is formed by, for example, changing the balance between isotropic etching by dry etching and anisotropic etching stepwise with respect to the base layer 18 made of the above-described dielectric formed on the transparent substrate 10. It can be formed. In this case, as shown in FIG. 1, the pedestal 12 is disposed on the base layer 18 formed on the transparent substrate 10. By forming the pedestal 12 in a trapezoidal shape, it is considered that an effect equivalent to that of a moth-eye structure in which the refractive index gradually changes can be obtained, light reflection can be prevented, and high transmittance characteristics can be obtained.

  The reflective layer 13 is formed on the pedestal 12 and is formed by arranging metal films extending in a band shape in the Y-axis direction that is the absorption axis. More specifically, the reflective layer 13 extends vertically from the pedestal 12 and has a rectangular shape when viewed from the predetermined direction, that is, in a cross-sectional view orthogonal to the predetermined direction. The reflection layer 13 functions as a wire grid polarizer, attenuates a polarized wave (TE wave (S wave)) having an electric field component in a direction parallel to the longitudinal direction of the reflection layer 13, and reflects the reflection layer 13. Transmits a polarized wave (TM wave (P wave)) having an electric field component in a direction orthogonal to the longitudinal direction.

  The constituent material of the reflective layer 13 is not particularly limited as long as it is a material having reflectivity with respect to light in the use band. For example, Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si , Ge, Te, etc., or an alloy containing one or more of these elements. Especially, it is preferable that the reflection layer 13 is comprised with aluminum or aluminum alloy. In addition to these metal materials, the reflective layer 13 may be composed of an inorganic film or a resin film other than a metal formed with a high surface reflectance by, for example, coloring.

  The film thickness of the reflective layer 13 is not particularly limited, and is preferably 100 nm to 300 nm, for example. The film thickness of the reflective layer 13 can be measured by, for example, the above-described electron microscopy.

  The width c of the reflective layer 13 is preferably equal to or smaller than the minimum width of the pedestal 12, and more preferably set smaller than the minimum width of the pedestal 12. Further, as will be described later, the width c of the reflective layer 13 is preferably smaller than the maximum width of the dielectric layer 14, that is, the grid width b which is the maximum width of the grid tip 17. Specifically, the ratio of the width c of the reflective layer 13 to the grid width b is preferably 52 to 72%. Note that these widths can be measured by, for example, the electron microscopy described above.

  As a method for making the width of the reflective layer 13 smaller than the width of the base 12 or the grid width (width of the dielectric layer 14) b, for example, isotropic etching by wet etching is exemplified. As described above, the reflective layer 13 reflects light, but by controlling the width of the reflective layer 13, the area of the reflective layer 13 viewed from the incident direction of the light is changed, and the light reflected by the reflective layer 13. The amount of changes. Therefore, the light transmission characteristics of the polarizing plate 1 can be controlled by controlling the ratio of the width of the reflective layer 13 to the grid width b.

  The dielectric layer 14 is formed on the reflective layer 13 and is formed by arranging dielectric films extending in a band shape in the Y-axis direction that is the absorption axis. The dielectric layer 14 is formed with a film thickness such that the polarization of the polarized light reflected by the absorbing layer 15 and transmitted by the absorbing layer 15 and reflected by the reflecting layer 13 is shifted by a half wavelength. Specifically, the film thickness of the dielectric layer 14 is appropriately set within the range of 1 to 500 nm, which can enhance the interference effect by adjusting the polarization phase. The film thickness of the dielectric layer 14 can be measured by, for example, the above-described electron microscopy.

Examples of the material constituting the dielectric layer 14 include Si oxides such as SiO ₂ , metal oxides such as Al ₂ O ₃ , beryllium oxide, bismuth oxide, MgF ₂ , cryolite, germanium, titanium dioxide, silicon, Common materials such as magnesium fluoride, boron nitride, boron oxide, tantalum oxide, carbon, or a combination thereof can be given. Especially, it is preferable that the dielectric material layer 14 is comprised with Si oxide.

The refractive index of the dielectric layer 14 is preferably larger than 1.0 and not larger than 2.5. Since the optical characteristics of the reflective layer 13 are also affected by the refractive index of the surroundings, the polarizing plate characteristics can be controlled by selecting the material of the dielectric layer 14.
Further, by appropriately adjusting the film thickness and refractive index of the dielectric layer 14, a part of the TE wave reflected by the reflection layer 13 can be reflected back to the reflection layer 13 when passing through the absorption layer 15. The light that has passed through the absorption layer 15 can be attenuated by interference. In this way, desired polarization characteristics can be obtained by selectively attenuating the TE wave.

The absorption layer 15 is formed on the dielectric layer 14, and is arranged extending in a band shape in the Y-axis direction that is the absorption axis. Examples of the constituent material of the absorption layer 15 include one or more kinds of substances having a light absorption action, such as metal materials and semiconductor materials, whose optical constants are not zero, and are appropriately selected depending on the wavelength range of light to be applied. Is done. Examples of the metal material include elemental elements such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, and Sn, or alloys containing one or more of these elements. Examples of the semiconductor material include Si, Ge, Te, ZnO, and silicide materials (β-FeSi ₂ , MgSi ₂ , NiSi ₂ , BaSi ₂ , CrSi ₂ , CoSi ₂ , TaSi, etc.). By using these materials, the polarizing plate 1 can obtain a high extinction ratio with respect to an applied visible light region. Especially, it is preferable that the absorption layer 15 is comprised including Si while containing Fe or Ta.

  When a semiconductor material is used as the absorption layer 15, the band gap energy of the semiconductor needs to be equal to or lower than the use band because the band gap energy of the semiconductor is involved in the absorption action. For example, in the case of using visible light, it is necessary to use a material having a wavelength of 400 nm or more, that is, a band gap of 3.1 ev or less.

The film thickness of the absorption layer 15 is not particularly limited, and is preferably 10 nm to 100 nm, for example. The film thickness of the absorption layer 15 can be measured by, for example, the above-described electron microscopy.
The absorption layer 15 can be formed as a high-density film by vapor deposition or sputtering. Moreover, the absorption layer 15 may be comprised from 2 or more layers from which a structural material differs.

  The polarizing plate 1 according to the present embodiment having the above configuration may have a diffusion barrier layer between the dielectric layer 14 and the absorption layer 15. That is, in this case, the lattice-shaped convex portion 11 includes a pedestal 12, a reflective layer 13, a dielectric layer 14, a diffusion barrier layer, and an absorption layer 15 in order from the transparent substrate 10 side. By having the diffusion barrier layer, diffusion of light in the absorption layer 15 is prevented. This diffusion barrier layer is made of a metal film such as Ta, W, Nb, or Ti.

  Further, in the polarizing plate 1 according to the present embodiment, the surface on the light incident side may be covered with a protective film made of a dielectric material in a range that does not affect the change in optical characteristics. Specifically, it is preferable that at least the side surface (inclined surface) of the grid tip 17 is covered with a protective film. The protective film is made of a dielectric film, and can be formed on the surface of the polarizing plate 1 (surface on which the wire grid is formed) by using CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition), for example. is there. Thereby, the oxidation reaction more than necessary for the metal film can be suppressed.

  Furthermore, in the polarizing plate 1 according to the present embodiment, the surface on the light incident side may be covered with an organic water-repellent film. Specifically, it is preferable that at least the side surface (inclined surface) of the grid tip portion 17 is covered with an organic water-repellent film. The organic water-repellent film is made of, for example, a fluorine-based silane compound such as perfluorodecyltriethoxysilane (FDTS), and can be formed by using, for example, the above-described CVD or ALD. Thereby, reliability, such as moisture resistance of the polarizing plate 1, can be improved.

[Production method of polarizing plate]
The manufacturing method of the polarizing plate 1 according to the present embodiment includes a base layer forming step, a reflective layer forming step, a dielectric layer forming step, an absorbing layer forming step, and an etching step.

  In the underlayer forming step, an underlayer is formed on the transparent substrate 10. In the reflective layer forming step, a reflective layer is formed on the base layer formed in the base layer forming step. In the dielectric layer forming step, a dielectric layer is formed on the reflective layer formed in the reflective layer forming step. In the absorbing layer forming step, an absorbing layer is formed on the dielectric layer formed in the dielectric layer forming step. In each of these layer forming steps, each layer can be formed by, for example, sputtering or vapor deposition.

  In the etching step, the lattice-shaped convex portions 11 arranged on the transparent substrate 10 at a pitch shorter than the wavelength of the light in the use band are selectively etched by the laminated body formed through the above-described respective layer forming steps. Form. Specifically, a one-dimensional lattice-like mask pattern is formed by, for example, a photolithography method or a nanoimprint method. And the lattice-like convex part 11 arranged on the transparent substrate 10 with a pitch shorter than the wavelength of the light of a use zone | band is formed by selectively etching the said laminated body. As an etching method, for example, a dry etching method using an etching gas corresponding to an object to be etched is used.

  In particular, in the present embodiment, a tapered shape in which the side surface of the grid tip portion 17 is inclined is formed by optimizing the etching conditions (gas flow rate, gas pressure, output, cooling temperature of the transparent substrate). Further, by optimizing the etching conditions, the base layer 18 is etched to form the pedestal 12 having a trapezoidal shape when viewed from the extending direction of the grid-like convex portions 11.

In addition, the manufacturing method of the polarizing plate 1 which concerns on this embodiment may have the process of coat | covering the side surface (inclined surface) of the grid front-end | tip part 17 with a protective film at least. Furthermore, the manufacturing method of the polarizing plate 1 according to the present embodiment may further include a step of covering at least the side surface (inclined surface) of the grid tip 17 with an organic water repellent film.
Thus, the polarizing plate 1 according to this embodiment is manufactured.

[Optical equipment]
The optical apparatus according to the present embodiment includes the polarizing plate 1 according to the present embodiment described above. Examples of the optical device include a liquid crystal projector, a head-up display, and a digital camera. Since the polarizing plate 1 according to the present embodiment is an inorganic polarizing plate that is superior in heat resistance compared to an organic polarizing plate, it is suitable for applications such as liquid crystal projectors and head-up displays that require heat resistance.

  When the optical apparatus according to the present embodiment includes a plurality of polarizing plates, at least one of the plurality of polarizing plates may be the polarizing plate 1 according to the present embodiment. For example, when the optical apparatus according to the present embodiment is a liquid crystal projector, at least one of the polarizing plates disposed on the incident side and the emitting side of the liquid crystal panel may be the polarizing plate 1 according to the present embodiment.

  According to the polarizing plate 1, the manufacturing method thereof, and the optical device described above, the following effects are exhibited.

  The polarizing plate 1 according to the present embodiment has a wire grid structure including a grid-like convex portion 11 having a pedestal 12, a reflective layer 13, a dielectric layer 14, and an absorption layer 15 in order from the transparent substrate 10 side. In the polarizing plate 1, by forming the pedestal 12 in a trapezoidal shape, an effect equivalent to that of the moth-eye structure in which the refractive index gradually changes in the pedestal 12 can be obtained. Therefore, it is considered that reflection of light can be further prevented and high transmittance characteristics can be obtained. Therefore, according to the present embodiment, it is possible to provide a polarizing plate 1 having high transmittance characteristics and excellent control of reflectance characteristics, a manufacturing method thereof, and an optical apparatus including the polarizing plate 1.

  In addition, this invention is not limited to the said embodiment, The deformation | transformation and improvement in the range which can achieve the objective of this invention are included in this invention.

  FIG. 4 is a schematic cross-sectional view showing a polarizing plate 1A according to Modification 1 of the present embodiment. In the grid-like convex portion 11A of the polarizing plate 1A, the width of the reflective layer 13A constituting the grid leg portion 16A and the maximum width (grid width) of the dielectric layer 14 constituting the grid tip portion 17 are the same. Except for this, the configuration is the same as that of the above embodiment. In the polarizing plate 1 </ b> A, the width of the reflective layer 13 </ b> A is the same as the minimum width of the pedestal 12.

  According to this polarizing plate 1A, as in the above embodiment, by forming the pedestal 12 in a trapezoidal shape, an effect equivalent to that of a moth-eye structure in which the refractive index of the pedestal 12 changes gently can be obtained. Therefore, it is considered that reflection of light can be further prevented and high transmittance characteristics can be obtained. Therefore, according to the polarizing plate 1A according to the first modification, it is possible to provide a polarizing plate 1A having a high transmittance characteristic and excellent in controlling the reflectance characteristic, a manufacturing method thereof, and an optical apparatus including the polarizing plate 1A. .

In the above embodiment, the boundary between the grid tip and the grid leg is at the boundary between the reflective layer and the dielectric layer, and the grid tip includes the dielectric layer and the absorption layer. Not limited. The grid tip may be configured with an absorption layer including a reflective layer and a dielectric layer, or may be configured only with an absorption layer. However, the transmittance of the TM wave transmitted through the polarizing plate can be greatly improved by including a reflective layer at the grid tip.
The application of the polarizing plate of the present embodiment is not limited to a liquid crystal projector. As a polarizing plate having a high transmittance power of polarized light in the transmission axis direction, it can be used for various applications.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Examples 1 and 2>
In Example 1, the polarizing plate 1 having the structure shown in FIG. 1 was used for the simulation. In Example 2, the polarizing plate 1A having the structure shown in FIG. 4 was used for the simulation. More specifically, the optical characteristics of these polarizing plates were verified by electromagnetic field simulation by the RCWA (Rigorous Coupled Wave Analysis) method. For the simulation, a grating simulator Gsolver manufactured by Grafting Solver Development was used. The simulations of the other embodiments described below are the same.

  FIG. 5 is a graph showing the results of verifying the transmission axis transmittance Tp of the polarizing plate 1 having the structure shown in FIG. 1 and the polarizing plate 1A having the structure shown in FIG. 4 by simulation. In FIG. 5, the horizontal axis indicates the wavelength λ (nm), and the vertical axis indicates the transmission axis transmittance Tp (%). Here, the transmission axis transmittance Tp means the transmittance of polarized light (TM wave) in the transmission axis direction (X-axis direction) incident on the polarizing plate. In FIG. 5, the reflective layer shown by a solid line whose width is narrower than the width of the dielectric layer represents the polarizing plate 1 of FIG. 1, and the width of the reflective layer shown by a broken line is the width of the dielectric layer. The same thing represents the polarizing plate 1A of FIG.

  As shown in FIG. 5, it was confirmed that both the polarizing plate 1 having the structure shown in FIG. 1 and the polarizing plate 1A having the structure shown in FIG. Further, by making the width of the reflective layer smaller (narrower) than the width of the dielectric layer, a visible light region extending from blue band light (λ = 430 to 510 nm) to red band light (λ = 600 to 680 nm). It was confirmed that the transmission axis transmittance Tp was improved as a whole.

<Example 3>
In Example 3, in the polarizing plate 1 having the structure shown in FIG. 1, the grid width is changed to 35 nm, 40 nm, 45 nm, 50 nm, and 55 nm, and the ratio of the width of the reflective layer in each grid width is changed. Was subjected to simulation. More specifically, the simulation was performed with respect to light in the green band (wavelength λ = 520 to 590 nm).

FIG. 6 is a graph showing the result of verifying the relationship between the width of the reflective layer of the polarizing plate 1 having the structure shown in FIG. 1 and the transmission axis transmittance Tp by simulation. More specifically, FIG. 6 shows the relationship between the ratio of the width of the reflective layer to the grid width and the transmission axis transmittance Tp. The horizontal axis indicates the width ratio (%) of the reflective layer, and the vertical axis indicates the transmission axis transmittance Tp (%).
FIG. 7 is a graph showing the result of verifying the relationship between the width of the reflective layer of the polarizing plate 1 having the structure shown in FIG. 1 and the contrast CR by simulation. More specifically, the relationship between the ratio of the width of the reflective layer to the grid width and the contrast CR is shown. The horizontal axis indicates the width ratio (%) of the reflective layer, and the vertical axis indicates the contrast CR.
Here, the contrast CR means the ratio of the transmission axis transmittance Tp to the absorption axis transmittance Ts (transmission axis transmittance Tp / absorption axis transmittance Ts). The absorption axis transmittance Ts means the transmittance of polarized light (TE wave) in the absorption axis direction (Y-axis direction) incident on the polarizing plate.

  As shown in FIG. 6, it can be seen that the transmission axis transmittance Tp increases as the grid width decreases. It can also be seen that if the grid width is the same, the transmission axis transmittance Tp increases as the ratio of the width of the reflective layer to the grid width decreases. For example, when the grid width is 35 nm and the ratio of the width of the reflective layer to the grid width is 100%, the grid width is 45 nm and the ratio of the width of the reflective layer to the grid width is about 67%. When compared with the case, substantially the same transmission axis transmittance Tp is obtained.

  As described above, it is difficult to reduce the grid width from the viewpoint of manufacturing variation, and it is difficult to maintain the reliability of the polarizing plate by reducing the grid width. On the other hand, according to the present embodiment, the transmission axis transmittance Tp corresponding to the grid width narrower than the actual grid width can be obtained by controlling the ratio of the width of the reflective layer to the grid width. Therefore, according to the present embodiment, it is not always necessary to narrow the grid width in accordance with desired light transmission characteristics, so that manufacturing variations can be suppressed and reliability can be improved.

  In addition, as shown in FIG. 7, it can be seen that the contrast CR also changes with any change in the ratio of the width of the reflective layer to the grid width (increase in the transmission axis transmittance Tp). Therefore, it can be seen that the transmittance characteristic of the polarizing plate is improved and an arbitrary contrast CR is obtained.

  By the way, as described above, there is a projector application as one of the applications of the polarizing plate. When a polarizing plate is used in a projector, since a higher transmission axis transmittance and higher contrast are required in recent years, the transmission axis transmittance Tp is preferably 93.5% or more (in FIG. 6). The contrast CR is preferably larger than 500 (refer to the CR target value in FIG. 7).

  Here, in each grid width, the ratio of the width of the reflective layer to the grid width when the transmission axis transmittance Tp is 93.5% or more, and the width of the reflective layer to the grid width when the contrast is 500 The ratio is shown in Table 1.

  As shown in Table 1, when the grid width is 45 nm, the ratio of the width of the reflective layer to the grid width when the contrast CR is 500 is the smallest. Therefore, in order to make the contrast CR larger than 500, it can be said that the ratio of the width of the reflective layer to the grid width is preferably about 50% or more.

  Further, the transmission axis transmittance Tp is 93.5% or more when the ratio of the width of the reflective layer to the grid width is 72.0% or less when the grid width is 35 nm. Similarly, when the grid width is 40 nm, the ratio of the width of the reflective layer to the grid width is 60.0% or less. When the grid width is 45 nm, the width of the reflective layer occupies the grid width. The ratio is 52.2% or less. Therefore, in order to set the transmission axis transmittance Tp to 93.5% or more, the grid width is in the range of 35 nm to 45 nm, and the ratio of the width of the reflective layer to the grid width is preferably X%. It can be said that the range is 52% to 72%.

  In this example, the simulation was performed for incident light having a green band light (wavelength λ = 520 to 590 nm). However, the incident light has a red band light (wavelength λ = 600 to 680 nm) or a blue band light ( Even if λ = 430 to 510 nm), the same result can be obtained although the ratio X% of the width of the reflective layer to the grid width is slightly different.

<Comparative Example 1>
FIG. 8 is a schematic cross-sectional view showing the polarizing plate 100 having no pedestal. The polarizing plate 100 has the same configuration as that of the polarizing plate 1A having the structure shown in FIG. 4 except that the lattice-shaped convex portion 101 does not have a pedestal and is directly provided on the base layer 108. In FIG. 8, the same reference numerals are given to the configurations common to the polarizing plate 1. The polarizing plate 100 having the structure shown in FIG. 8 was used for the simulation.

FIG. 9 is a graph showing the results of verifying the transmission axis transmittance Tp of the polarizing plate 1A having the structure shown in FIG. 4 and the polarizing plate 100 having the structure shown in FIG. 8 by simulation. In FIG. 9, the horizontal axis indicates the wavelength λ (nm), and the vertical axis indicates the transmission axis transmittance Tp (%). In addition, in FIG. 9, the one having a trapezoidal pedestal indicated by a solid line represents the polarizing plate 1A in FIG. 4, and the one having no pedestal indicated by a broken line represents the polarizing plate 100 in FIG.
As shown in FIG. 9, by having a trapezoidal base, the transmission axis transmittance Tp is improved from light in the blue band (λ = 430 to 510 nm) to light in the green band (wavelength λ = 520 to 590 nm). It was confirmed that

<Example 4>
FIG. 10 is a schematic cross-sectional view showing the polarizing plate 1B having a rectangular grid tip portion 17B. The polarizing plate 1B of Example 4 is the same as the polarizing plate 1 having the structure shown in FIG. 1 except that the grid tip portion 17B is not a tapered shape but a rectangular dielectric layer 14B and an absorption layer 15B. It is a configuration. In FIG. 10, the same reference numerals are assigned to configurations common to the polarizing plate 1. The polarizing plate 1B corresponds to the polarizing plate 1 having a tilt angle θ of 90 degrees on the side surface of the grid tip of the polarizing plate 1 shown in FIG.
In this example, the polarizing plate 1 having the structure shown in FIG. 1 was subjected to the simulation by changing the tilt angle θ and variously changing the ratio of the height a of the grid tip and the grid width b. In this example, simulations of transmission axis transmittance Tp and absorption axis reflectance Rs were performed. Here, the absorption axis reflectance Rs means the reflectance of polarized light (TE wave) in the absorption axis direction (Y-axis direction) of the polarizing plate. In this example, a simulation was performed on a polarizing plate designed to be optimized for light in the green band (wavelength λ = 520 to 590 nm (predetermined wavelength)).

  FIG. 11 shows the tilt angle θ of the grid tip and the transmission axis transmittance when the ratio of the height a of the grid tip to the grid width b is a: b = 6: 9 in the polarizing plate having the structure shown in FIG. It is a graph which shows the result of having verified the relationship with Tp by simulation. In FIG. 11, the horizontal axis indicates the inclination angle θ (°), and the vertical axis indicates the transmission axis transmittance Tp (%). In FIG. 11, the broken line indicates light in the blue band (wavelength λ = 430 to 510 nm), the solid line indicates light in the green band (wavelength λ = 520 to 590 nm), and the one-dot chain line indicates the red band. The light of wavelength (λ = 600 to 680 nm) is shown.

  Here, if the transmission axis transmittance Tp is high, it means that high intensity desired light is transmitted through the polarizing plate. As shown in FIG. 11, the blue band (wavelength λ = 430 to 510 nm) and the green band (wavelength λ = 520 to 590 nm) as the tilt angle θ tilts from 90 degrees (that is, from the right to the left on the graph). ) And the red band (wavelength λ = 600 to 680 nm), the transmission axis transmittance Tp is high. In particular, for the blue band, it can be seen that the increase in the transmission axis transmittance Tp is large.

FIG. 12 shows the inclination angle θ and the absorption axis reflectivity of the grid tip when the ratio of the height a of the grid tip to the grid width b is a: b = 6: 9 in the polarizing plate having the structure shown in FIG. It is a graph which shows the result of having verified the relationship with Rs by simulation. In FIG. 12, the horizontal axis indicates the inclination angle θ (°), and the vertical axis indicates the absorption axis reflectance Rs (%).
As shown in FIG. 12, when the absorption axis reflectance Rs increases, it means that the polarized light (TE wave) in the absorption axis direction reflected by the polarizing plate becomes stronger. Since such reflected light lowers the extinction ratio, the absorption axis reflectance Rs is preferably low. In many liquid crystal projector applications, the absorption axis reflectance Rs is required to be less than 10%.

  According to FIG. 12, the smaller the tilt angle θ, the higher the absorption axis reflectivity Rs in the green band, which is the design wavelength of the polarizing plate in this simulation, and the absorption axis reflectivity Rs becomes smaller when the tilt angle θ is smaller than 61 degrees. Over 10%. Therefore, the value of the tilt angle θ allowed for the liquid crystal projector application is 61 degrees ≦ θ <90 degrees. This angle is called a device characteristic tilt angle. When the inclination of the side surface of the grid tip is increased (decreasing the inclination angle θ), the absorption axis reflectivity Rs increases because the size of the dielectric layer and the absorption layer along the transparent substrate decreases. For this reason, it is considered that the absorption effect of the reflected light (TE wave) by these decreases.

  13 and 14 show the case where the ratio between the height a of the grid tip and the grid width b is a: b = 8: 11, and FIGS. 15 and 16 show the height a and the grid width of the grid tip. 17 and FIG. 18 show the case where the ratio of the height a of the grid tip and the grid width b is a: b = 10: 9 when the ratio to b is 8: 9. Are the transmission axis transmittance Tp and absorption axis reflection of the polarizing plate with respect to the inclination angle θ of the grid front end when the ratio of the height a of the grid front end to the grid width b is a: b = 8: 7, respectively. It is a graph which shows rate Rs.

  Regardless of the ratio of the height a of the grid tip and the grid width b, the greater the slope of the side surface of the grid tip (the smaller the tilt angle θ), the blue band, the green band, and the red band. Also, an improvement in the transmission axis transmittance Tp was observed. In any case, it was found that the transmission axis transmittance Tp in the blue band was larger than that in the other bands.

  On the other hand, when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 7, as shown in FIG. 20, when θ <77 degrees, the absorption axis of light of the wavelength in the green band is obtained. The reflectance Rs exceeds 10%. Therefore, the device characteristic tilt angle in this case is 77 degrees ≦ θ <90 degrees. Further, when the ratio of the height a of the grid tip to the grid width b is a: b = 8: 9, the transmission axis transmittance Tp is improved by tilting the side surface of the grid tip as shown in FIG. The effect is high, and the inclination angle θ can be set to 60 ° ≦ θ <90 °.

  Here, based on the simulation results of FIGS. 11 to 20, Table 2 shows the range of the inclination angle θ of the grid tip with respect to the ratio of the height a of the grid tip and the grid width b.

  In Table 2, the simulation tilt angle θ is the range of the tilt angle where the simulation was performed, and as described above, the range is θo ≦ θ <90 degrees (θo = arctan (2a / b)). 11-20, when the ratio of the height a and the grid width b is represented by a / b in the shape of the tip of the grid, in any range included in 2/3 ≦ a / b ≦ 8/7, the above It was confirmed that the transmission axis transmittance of light in each wavelength band is high in the range of the inclination angle θ. Further, as described above, the device characteristic inclination angle is an inclination angle in a range where the absorption axis reflectance Rs does not exceed 10%. When the polarizing plate is used in a liquid crystal projector or the like, it is desirable that the tilt angle θ satisfies the device characteristic tilt angle range.

<Example 5>
Next, a polarizing plate having a wire grid structure shown in FIG. 1 was actually produced, and the obtained optical characteristics were compared with simulation results. FIG. 21 compares the measured value of the transmission axis transmittance Tp with respect to the inclination angle θ of the side surface of the grid tip and the simulation result when the ratio of the height a of the grid tip to the grid width b is 8: 9. It is a graph which shows the result verified by doing.

  In FIG. 21, the outline points are the same as the simulation results shown in FIG. On the other hand, when the average value of the inclination angle θ is 77 degrees and 74 degrees, the actual measurement values are indicated by black dots. Here, when the average value of the inclination angle θ is 74 degrees, the actual measurement value of the blue band (wavelength λ = 430 to 510 nm) and the actual measurement value of the green band (wavelength λ = 520 to 590 nm) are around 92.6%. It is a point that overlaps. The average value of the inclination angle θ is because there is variation in the inclination angle of the side surface of the grid tip of the actually produced polarizing plate.

  As can be seen from FIG. 21, also in the actual measurement results, the transmission axis transmittance Tp is higher in all bands when the average value of the inclination angle θ is 74 degrees than when the average value of the inclination angle θ is 77 degrees. It is high. Particularly in the blue band, the transmission axis transmittance Tp is significantly improved. Thus, it was confirmed that the transmission axis transmittance Tp is improved by further tilting the side surface of the grid tip (by reducing the tilt angle θ).

  Next, FIGS. 22 to 25 show measured values of the transmission axis transmittance Tp, the absorption axis transmittance Ts, the transmission axis reflectance Rp, and the absorption axis reflectance Rs, respectively, for the two actually manufactured polarizing plates. It is a graph. Here, the transmission axis reflectance Rp means the reflectance of polarized light (TM wave) in the transmission axis direction (X-axis direction) incident on the polarizing plate. In each graph, the polarizing plate indicated by a broken line has an inclination angle θ of the side surface of the grid tip of 80 to 84 degrees, and the polarizing plate indicated by a solid line represents the inclination angle θ of the side surface of the grid tip. Is in the range of 76-80 degrees. The ratio between the grid height a and the grid width b of the two polarizing plates is close to 2/3 and 8/11.

  The transmission axis transmittance Tp indicating the TM wave transmittance of the polarizing plate shown in FIG. 22 is greatly increased particularly in the blue band (wavelength λ = 430 to 510 nm) when the inclination angle θ of the side surface of the grid tip is reduced. Improvement is recognized. In addition, when the value of the inclination angle θ is 76 to 80 degrees, the transmission axis transmittance Tp is substantially constant at about 92% to 93% regardless of the wavelength in the visible light region including the blue band having a wavelength of 430 nm or more. Thus, a sufficient improvement in transmittance is obtained. Therefore, when the inclination angle θ is 80 degrees or less, it is considered that the effect of improving the transmittance according to the present invention is great. In the simulation examples shown in FIGS. 11, 15, and 17, if the inclination angle θ is 80 degrees or less, the difference between the transmission axis transmittances Tp of the blue band, the green band, and the red band is 0. It is a small value in the range of about 5 to 1%. For this reason, since it permeate | transmits equally for every wavelength range | band of the light which permeate | transmitted the polarizing plate, there is little change of a color.

  On the other hand, for the absorption axis transmittance Ts indicating the transmittance of the TE wave shown in FIG. 23 and the transmission axis reflectance Rp indicating the reflectance of the TM wave shown in FIG. But it is hardly affected. Further, with respect to the absorption axis reflectance Rs indicating the reflectance of the TE wave shown in FIG. 25, the reflectance tends to decrease over the entire visible light.

  Based on the above results, a trapezoidal pedestal is formed on the transparent substrate in the grid-like convex portion of the wire grid structure, and the width of the reflective layer is controlled to be narrower than the width of the pedestal and the dielectric layer. By controlling the inclination angle, it can be said that the effect of improving the transmittance in the transmission axis direction, particularly the light on the short wavelength side including the blue band in the visible light region, is great.

  In addition, although the basic structure is the same as that of the prior art, a desired light transmission characteristic corresponding to a narrow grid width can be obtained without narrowing the grid width itself, so photolithography by forming a thin grid. The mask pattern collapses due to, etc., or the grid collapse due to dry etching or the like hardly occurs. Thereby, manufacture of a polarizing plate can be made easy, manufacturing variation can be suppressed collectively, and the reliability as a polarizing plate can also be maintained.

DESCRIPTION OF SYMBOLS 1, 1A, 1B Polarizing plate 10 Transparent substrate 11, 11A, 11B Grid-shaped convex part 12 Base 13, 13A Reflective layer 14, 14B Dielectric layer 15, 15B Absorbing layer 16, 16A Grid leg part 17, 17B Grid front-end | tip part 18 Underlayer P Pitch of grid convex part a Height of grid tip b Grid width c Reflective layer width θ Inclination angle

Claims (15)

A polarizing plate having a wire grid structure,
A transparent substrate;
A grid-like convex portion arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use band and extending in a predetermined direction,
The lattice-like convex part has, in order from the transparent substrate side, a pedestal, a reflective layer, a dielectric layer, and an absorption layer,
A polarizing plate having a trapezoidal shape when the pedestal is viewed from the predetermined direction.   The polarizing plate according to claim 1, wherein a minimum width of the pedestal is equal to or greater than a width of the reflective layer.   The polarizing plate according to claim 1, wherein the pedestal is made of a Si oxide that is transparent with respect to the wavelength of light in a use band.   The grid front end portion formed at the front end of the lattice-shaped convex portion has a tapered shape whose side surface is inclined in a direction in which the width becomes narrower toward the front end side when viewed from the predetermined direction. The polarizing plate as described. The grid tip is composed of the dielectric layer and the absorbing layer,
The maximum width of the grid tip is 35 to 45 nm,
The polarizing plate according to claim 4, wherein a width of the reflective layer is 52 to 72% with respect to a maximum width of the grid tip. The inclination angle of the side surface of the grid tip with respect to the transparent substrate is θ,
When the height of the grid tip when viewed from the predetermined direction is a, the maximum width of the grid tip is b, and θ ₀ = arctan (2a / b),
2/3 ≦ a / b ≦ 8/7 and θ ₀ ≦ θ <90 degrees,
6. The polarizing plate according to claim 4, wherein the tilt angle θ is selected from an angle range in which the reflectance in the absorption axis direction of light having a predetermined wavelength in the visible light region is 10% or less.   The inclination angle θ is defined as an inclination angle of a tangent to the side surface of the grid tip at the center position in the height direction of the grid tip when viewed from the predetermined direction, and the angle range is θ ≦ 80. The polarizing plate according to claim 4, which has a degree.   The polarizing plate according to claim 1, wherein the transparent substrate is transparent with respect to the wavelength of light in a use band and is made of glass, crystal, or sapphire.   The polarizing plate according to claim 1, wherein the reflective layer is made of aluminum or an aluminum alloy.   The polarizing plate according to claim 1, wherein the dielectric layer is made of Si oxide.   The polarizing plate according to claim 1, wherein the absorption layer includes Fe or Ta and includes Si.   The polarizing plate according to claim 1, wherein a surface of the polarizing plate on which light is incident is covered with a protective film made of a dielectric.   The polarizing plate according to claim 1, wherein a surface of the polarizing plate on which light is incident is covered with an organic water-repellent film. A method of manufacturing a polarizing plate having a wire grid structure,
An underlayer forming step of forming an underlayer on a transparent substrate;
A reflective layer forming step of forming a reflective layer on the underlayer;
A dielectric layer forming step of forming a dielectric layer on the reflective layer;
An absorption layer forming step of forming an absorption layer on the dielectric layer;
An etching step of forming a grid-like convex portion arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use band by selectively etching the formed laminate, and
In the etching step, the base layer is etched to form a pedestal having a trapezoidal shape when viewed from the extending direction of the grid-like convex portions.   An optical apparatus comprising the polarizing plate according to claim 1.

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