JPH10332932A - Filter polarizing light in specific wavelength range - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the polarizing filter which can polarize light of large irradiation area in a specific wavelength range, has high heat resistance, and does not vary in transmissivity with heat. SOLUTION: The filter which polarizes light in the specific wavelength range is formed by alternately layering a film which has optical anisotropy of optical thickness 1/4 as large as desired wavelength to be polarized and a film which has isotropy. This multi-layered film 3 has no difference in refractive index between the layers to light whose electric field vibrates in an (x) direction and operates as a single-layer film having a specific refractive index and also operates as a multi-layered film having different-refractive-index films laminated by turns to light whose electric field vibrates in a (y) direction orthogonal to the (x) direction. Therefore, when light of the specific wavelength to be polarized (light having wavelength 1/4 as large as the optics thickness of the film) is made incident on this multi-layered film 3, the light whose electric field vibrates in the (x) direction is transmitted and the light whose electric field vibrates in the (y) direction has mutual interference between reflected lights on the border surfaces of the respective layers, so that transmitted light is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for polarizing light in a specific wavelength range, and more particularly to a filter for polarizing light having a relatively large area suitable for forming an alignment film of a liquid crystal substrate. Related to a polarizing filter.

[0002]

2. Description of the Related Art In recent years, in the production of liquid crystal substrates, a method using polarized light has been proposed as one of techniques for aligning liquid crystal without rubbing. In this method, a thin film of a polyimide resin or the like is irradiated with polarized light to chemically change a polymer in a specific direction of the thin film so as to align the alignment. Ultraviolet rays having a wavelength of about 365 nm have a large effect on the alignment. However, in order to apply the above technique to the formation of the alignment film on the liquid crystal substrate, a large polarizing filter is required. That is, when manufacturing a liquid crystal display element, usually four to six liquid crystal display elements are formed on one substrate, and the size of the substrate to be irradiated with light is usually 550 m.
It is about mx 650 mm. For this reason, as the irradiation region of the polarized light used for forming the alignment film of the liquid crystal substrate, 80
0 mm × 800 mm is required. Conventionally, there has been no polarizing element suitable for forming the above-mentioned alignment film of the liquid crystal substrate.

[0003]

As the polarizing element, the following polarizing elements (1) and (2) are known.
The polarizing element (2) has the following problems, and is not preferable for application to the formation of the alignment film of the liquid crystal substrate described above. (1) Cube-type polarizing element As shown in FIG. 6, two rectangular prisms exhibiting birefringence face each other with inclined surfaces facing each other.
There are a Taylor polarizing prism, a Gran Thomson polarizing prism, and the like.

Since the cube-type polarizing element has the shape shown in FIG. 6, when trying to polarize light of a large area, the volume of the cube increases, and the device for mounting the cube also increases. Therefore, it is not suitable for forming an alignment film of the liquid crystal substrate which requires a large-area irradiation region. In the Grand Taylor polarizing prism and the Gran Thomson polarizing prism, light (ordinary ray) not emitted from the prism is absorbed by a black polymer that is a mounting material provided in the housing. For this reason, when a laser having a power of 2 W or more in continuous oscillation is used, there is a problem that the black polymer is eroded by the ordinary light and the prism is peeled off.

(2) Polarizing element using organic film This is a polarizing element having an organic film formed on a substrate. Due to the bonding structure of molecules constituting the film, only light of a specific polarization component is transmitted and light of the remaining components is Absorbed by the membrane. 280 nm
When polarizing light in the wavelength range of about 2 μm, the film is used at a temperature of 95 ° C. or less. 100 ° C film temperature
Above this, the film is altered and the transmittance is reduced. If the film is used for a long time, the film absorbs light energy and the temperature of the film increases, so that the film cannot be used for a long time. In addition, the organic film usually absorbs a large amount of light having a wavelength of 400 nm or less, and the transmittance is reduced. That is, the polarization efficiency of light in the ultraviolet region is poor.

On the other hand, formation of an alignment film on a liquid crystal substrate requires irradiation of relatively intense light energy onto the substrate surface.
It is also desirable that the wavelength region is ultraviolet light near 365 nm as described above. Therefore, the polarizing element using the organic film cannot satisfy the conditions required for forming the alignment film of the liquid crystal substrate. The present invention has been made in view of the above-described circumstances, and its purpose is to
A filter that polarizes light in a specific wavelength range that can polarize light with a large irradiation area. It has high heat resistance, does not change its transmittance due to heat, and is used for a long time in a region where light energy is strong. Another object of the present invention is to provide a polarizing filter which can be applied to the apparatus and which does not extremely increase the size of a device to which the polarizing filter is applied.

[0007]

Means for Solving the Problems When depositing a thin film on a substrate, as shown in FIG. 7 (a), a transparent substrate is arranged perpendicularly to the direction in which deposition particles fly, and the film is deposited. ,
Light incident perpendicularly to the film has the same refractive index in any direction (this is called an isotropic film). On the other hand, as shown in FIG. 7B, when a film is deposited by disposing the transparent substrate at an angle to the direction in which the deposition particles fly, a film having a columnar structure as shown in FIG. Grows. This columnar structure is dense in a direction perpendicular to the plane formed by the direction of the deposition particles and the normal of the substrate (hereinafter, this direction is referred to as the x direction), in a direction parallel to the substrate and perpendicular to the x direction. (Hereinafter, this direction is referred to as the y direction). For this reason, the deposited film has an x-direction and a y-direction.
The refractive index differs depending on the direction, and the substrate has optical anisotropy. (The method of depositing a film on a substrate by arranging the substrate at an angle to the direction in which the deposited particles fly is referred to as "oblique deposition." ).

When light is incident on a film having optical anisotropy as described above, the phase shifts depending on the direction of vibration of the electric field of light. A film having the above optical anisotropy utilizing this property,
Conventionally, it has been used as a quarter-wave plate, a half-wave plate, or the like as an optical phase plate. Here, the refractive index in the x direction is nx,
Assuming that the refractive index in the y direction is ny and | nx−ny | = Δn, “Δn × the physical thickness of the film” is 1 of the wavelength of the incident light.
In the case of / 4, the wavelength becomes a 波長 wavelength plate, and in the case of の of the wavelength of incident light, the wavelength becomes a （wavelength plate. , No.7,19
95, pages 32-35).

According to the present invention, a filter for polarizing light in a specific wavelength range is formed by the above-described oblique deposition method, and attention is paid to the fact that a film having optical anisotropy can be formed by the oblique deposition method. As shown in FIG. 1 (a), a film having a specific wavelength range is obtained by alternately stacking a film having an optical anisotropy having an optical thickness of of the thickness and a film having an isotropic property as a multilayer. Is formed. The optical thickness is “physical thickness of film × refractive index”. Here, when the vapor deposition film is formed by the oblique vapor deposition method, the thickness of the anisotropic film becomes a slope shape with one end being thicker than the other end, but in the present invention, as shown in FIG. The optical thickness (1/4 of the wavelength to be polarized) is defined by the thickness at the substantially central portion of the anisotropic film.

The multilayer film formed as described above has no difference in refractive index between the layers with respect to light whose electric field oscillates in the x direction, and acts as a single layer having a predetermined refractive index. For light whose electric field oscillates in the y direction perpendicular to the direction, it acts as a multilayer film in which films having different refractive indexes are alternately stacked. Therefore, when light of a predetermined wavelength to be polarized (light having a wavelength of 1/4 of the optical thickness of the film) is incident on the multilayer film formed in this manner, the multilayer film shown in FIGS. As shown in the figure, light whose electric field oscillates in the x direction is transmitted, but y
Since the refractive index of each layer is different with respect to the light whose electric field oscillates in the direction, the reflected light at the interface between the layers interferes with each other and strengthens each other to reduce the transmitted light.

This is due to the following characteristics of the optical thin film.
Light reflects at interfaces with different refractive indices. Here, when light having a wavelength λ is incident on a film having an optical thickness of １ ／ of the wavelength λ, if the phase of the incident light at the interface on the light incident side of the film is 0 °, the incident light is The light is reflected at the interface on the side opposite to the light incident side of the film, and has a phase of 180 ° when it reaches the interface on the light incident side again. On the other hand, at the interface between the low-refractive-index layer and the high-refractive-index layer, when light incident from the low-refractive-index layer is reflected, the phase of the reflected light at the interface is relative to the phase of the incident light at the interface. Inversion (180 ° out of phase)
Happens. That is, the phase of the incident light at the interface is set to 0.
In this case, the phase of the reflected light at the interface becomes 180 °. Therefore, when the refractive index for the wavelength λ of the adjacent medium of the film having the optical thickness of １ ／ of the wavelength λ is lower than the refractive index for the wavelength λ of the film, that is, on the light incident side of the film. When the interface is the interface from the low refractive index layer to the high refractive index layer, and the interface on the opposite side of the film from the light incident side is the interface from the high refractive index layer to the low refractive index layer, the light incident on the film Assuming that the phase of the incident light at the interface on the side is 0 °, the phase of the light reflected at the interface at the interface is 180 °. On the other hand, when the incident light is reflected at the interface of the film opposite to the light incident side and reaches the interface on the light incident side again, the phase also becomes 1
80 °. Therefore, the phase of the reflected light at the interface of the film on the light incident side coincides with the phase of the reflected light at the interface of the film on the side opposite to the light incident side. (For the properties of optical thin films, see, for example,
Name translation, Nikkan Kogyo Shimbun, published on November 30, 1989, "Optical Thin Film", pp. 6-11, edited by Shiro Fujiwara, edited by Kozo Ishiguro and two others, Kyoritsu Shuppan Co., Ltd., published on February 25, 1985, Optical technology series 11 “Optical thin film” See pages 12 to 15).

Accordingly, when films having different refractive indexes are alternately laminated, and light having a wavelength λ at which an electric field vibrates in the y direction is incident on a multilayer film having an optical thickness of 層 of the wavelength λ, As shown in FIG. 1 (c), the reflected light at each interface returns on the incident surface of the multilayer film in a state where the phases are aligned, and these components are recombined so as to reinforce each other. Therefore, as the number of layers increases, a large amount of reflected light having the same phase is reflected, the intensity of the reflected light increases, and the intensity of the transmitted light decreases accordingly. However, this multilayer film transmits light other than the predetermined wavelength λ regardless of the x direction and the y direction. Materials for forming the above-mentioned deposited film include tantalum pentoxide (Ta ₂ O ₅ ), hafnium oxide ₂ (HfO ₂ ),
Tungsten trioxide (WO ₃ ), cerium dioxide (Ce)
O ₂ ) and zirconium dioxide (ZrO ₂ ) can be used.

In the invention of claims 1 to 3 of the present invention,
As described above, a film of a specific wavelength range is polarized by alternately superimposing a film having optical anisotropy and an isotropic film having an optical thickness of 1/4 of the wavelength to be polarized. Since the necessary filter is provided, a polarizing element having an arbitrary size corresponding to the irradiation area can be manufactured if necessary deposition equipment is prepared. In addition, since the polarizing element can be formed by a flat plate, the size of a device to be applied is not increased. Further, since the multilayer film is formed by a vapor-deposited film, heat resistance is high, and optical characteristics such as transmittance are not degraded by heat, so that it can be used in a region where light energy is strong.
Furthermore, since it is formed of a vapor-deposited film, light in the ultraviolet region (240 nm to 400 nm) can be polarized.

[0014]

Embodiments of the present invention will be described below. (1) Formation of vapor-deposited film FIG. 2 is a view for explaining a method of forming a vapor-deposited film according to the present invention. In FIG.
Reference numeral 2 denotes an evaporation source that emits evaporation particles, and a filter for polarizing light in a specific wavelength range is manufactured as follows. (a) As shown in FIG. 3A, the transparent substrate 1 is arranged to be inclined (inclination angle: + α) with respect to the direction in which the vapor deposition particles fly, and the optical thickness is １ ／ of the wavelength to be polarized. A (physical thickness × refractive index) film is deposited. The film thus deposited has the property of optical anisotropy as described above. When oblique vapor deposition is performed as described above, the vapor deposition film on the substrate is thicker near the vapor deposition source and thinner farther away, as described above.

(B) As shown in FIG. 1 (b), a transparent substrate 1 on which an anisotropic film is deposited is arranged perpendicular to the direction in which the deposited particles fly, and the wavelength of light to be polarized is 1 A film having an optical thickness of / 4 is deposited. The film thus deposited has optically isotropic properties as described above. (c) As shown in FIG. 3 (c), the transparent substrate 1 on which the isotropic film is formed is inclined (inclination angle: -α) with respect to the direction in which the vapor deposition particles fly, and polarized. 1/4 of the desired wavelength
A film having an optical thickness of is deposited. (d) A film having optically isotropic properties is formed in the same manner as in (b) above. (e) The above processes (a) to (d) are repeated to form a multilayer film in which optically anisotropic films and optically isotropic films are alternately deposited.

At the time of oblique deposition, the thickness of the deposited film is thicker near the deposition source and thinner farther away from the deposition source, as described above. As a result, the reflection bands are shifted at both ends of the film. Although the width of the reflection band does not change, the entire reflection band moves in parallel to the long wavelength region or the short wavelength region. The width of the reflection band is defined by a wavelength width W at a transmittance intermediate between the maximum value Tmax and the minimum value Tmin of the transmittance, as shown in FIG. So, as mentioned above,
After obliquely vapor-depositing the substrate 1 at an angle of α with respect to the direction in which the vapor-deposited particles fly, vapor deposition is performed with the substrate 1 perpendicular to the direction in which the vapor-deposited particles fly, and then the substrate 1 is moved in the direction in which the vapor-deposited particles fly. -Oblique deposition with an inclination of α. By performing the above-described vapor deposition, a multilayer film as shown in FIG. 3 is formed, and the thickness of both ends of the formed multilayer film becomes the same.

Further, at the time of oblique deposition, the angle α for tilting the substrate
Is determined based on the magnitude of Δn [= (refractive index nx in x direction) − (refractive index in y direction is ny)].
The larger Δn is, the wider the reflection band is, and the higher the reflection efficiency can be obtained with a smaller number of layers, which is advantageous in optical characteristics. Tantalum pentoxide (Ta)
_In the case of the ₂ O ₅ ) film, it has been experimentally confirmed that the inclination angle is optimally about 70 ° in order to obtain a large Δn.

When light having a wavelength four times the optical thickness of the film is incident on the multilayer film formed as described above, light whose electric field oscillates in the x direction is transmitted as described above, but y light is transmitted. With respect to light whose electric field oscillates in the direction, the transmitted light decreases because the refractive index of each layer is different, and functions as a polarizing element for light in a specific wavelength range. In the formation of the above-mentioned vapor deposition film, the same oblique vapor deposition of (a), ordinary vapor deposition of (b) → oblique vapor deposition of (c) → ordinary vapor deposition of (d) were repeated using the same vapor deposition substance. A multilayer film may be formed, or the x direction, y
As long as the refractive indices in the directions match, the same effect can be obtained even when vapor deposition is performed using a plurality of substances.

(2) Specific Example The following method was used to form a multilayer film as described above. - deposited film: 5 oxide 2 tantalum (Ta ₂ O ₅₎ · further optical thickness: 100 [mu] m, number of layers: 31 layers & anisotropic film y-direction of the refractive index of (ny): 1.59 (Wavelength 397nm 4) The refractive index (nx) of the anisotropic film in the x direction and the refractive index of the isotropic film: 1.72 (at a wavelength of 396 nm) FIG. 4 shows the transmittance of the multilayer film in the x and y directions. As shown in the figure, a multilayer film transmitting only the light whose electric field oscillates in the x direction out of the light of 400 nm was able to be formed. By irradiating the multilayer film with light containing ultraviolet light, polarized light having a predetermined wavelength could be obtained in a region having a wavelength of 400 nm or less.

(3) Application Example FIG. 5 is a diagram showing an example of the configuration of a polarized light irradiation device using a polarizing filter formed of a multilayer film according to the present invention. As shown in FIG. 1, the polarized light irradiating apparatus includes a discharge lamp 11 such as an ultra-high pressure mercury lamp, an elliptical converging mirror 12, and a first plane mirror 1
3, the integrator lens 15, the shutter 14, and the second
, A filter 18 for transmitting light of a specific wavelength, and a polarizing filter 19 formed of the above-mentioned multilayer film.

In FIG. 1, light including ultraviolet light emitted from a discharge lamp 11 is condensed by an elliptical converging mirror 12, reflected by a first plane mirror 13, and incident on an integrator lens 15 via a shutter 14. . Integrator lens 15
Is further reflected by the second plane mirror 16, is converted into parallel light by the collimator lens 17, and is incident on the polarization filter 19 through the filter 19 that transmits light of a specific wavelength. As described above, the polarizing filter 19 transmits only light whose electric field oscillates in the x direction and reduces transmitted light of light whose electric field oscillates in the y direction, for light in a specific wavelength range, as described above. Therefore, of the light in the specific wavelength range that has passed through the filter 18, only the light whose electric field oscillates in the x direction passes through the polarizing filter 19 and irradiates the work W such as a liquid crystal substrate through the mask M. . Reference numeral 20 denotes an alignment microscope for aligning the mask M and the work W,
1 is a work stage, and work stage 21 is X,
The work stage 21 is movable in the Y, Z, and θ directions.
The work is placed on the top. Note that the X axis is an axis parallel to the work surface, the Y axis is an axis parallel to the work surface and orthogonal to the X axis, the Z axis is an axis orthogonal to the X and Y axes, and θ is a rotation about the Z axis. .

Next, the photo-alignment treatment of the alignment film of the liquid crystal display device using the polarized light irradiation device shown in FIG. 5 will be described.
By irradiating the entire surface of the thin film of the liquid crystal substrate that is not aligned with polarized light as described below, the entire surface of the thin film of the liquid crystal substrate can be optically aligned. (a) In FIG. 5, the work W is placed on the work stage 21. When irradiating the entire surface of the substrate with polarized light, the mask M is not used. Further, a mask M that transmits light only in the thin film portion of the liquid crystal substrate may be used. (b) The work stage 21 is rotated about the Z axis so that the polarization direction is oriented in a predetermined direction with respect to the work W.
When the mask M is used, the mask M is set on a mask stage (not shown), and the alignment mark between the mask M and the work W is observed with an alignment microscope.
The work stage 21 is driven in the X, Y, and θ directions to position the mask M and the work W so that the alignment marks of the mask M and the work W match. In this case, the orientation of the mask M may be set in advance so as to match the polarization direction.

(C) The shutter 14 is opened, and the work W is irradiated with polarized light for a predetermined time. In the above description, the case where the entire surface of the thin film of the liquid crystal substrate is irradiated with the polarized light has been described. However, the polarized light is irradiated through a mask on a part of the liquid crystal substrate on which the alignment film has already been formed by rubbing or optical alignment. Irradiation can also change the alignment characteristics.

[0024]

As described above, in the present invention, a filter for polarizing light in a specific wavelength range is obtained by alternately superposing a film having optical anisotropy and a film having isotropic properties in a multilayer. Thus, the following effects can be obtained. (1) If necessary vapor deposition equipment is prepared, a polarizing element having an arbitrary size according to an irradiation area can be manufactured. In addition, since the polarizing element can be formed by a flat plate, the size of a device to be applied is not increased. (2) Since a multilayer film is formed by a vapor-deposited film, heat resistance is high, optical characteristics such as transmittance are not deteriorated by heat, and it can be used in a region where light energy is strong. (3) Since the polarizing element is formed of a vapor-deposited film, the light in the ultraviolet region (240 nm to 400 nm) can be polarized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a polarizing element and an operation thereof according to the present invention.

FIG. 2 is a diagram illustrating a method for forming a vapor deposition film in the present invention.

FIG. 3 is a diagram illustrating the relationship between the inclination of a substrate and the thickness of a deposited film.

FIG. 4 is a diagram illustrating characteristics of a polarizing element according to an example of the present invention.

FIG. 5 is a diagram showing an example of a configuration of a polarized light irradiation device using the polarizing element of the present invention.

FIG. 6 is a diagram showing a configuration of a cube-type polarizing element.

FIG. 7 is a diagram illustrating an oblique vapor deposition method.

FIG. 8 is a diagram illustrating a columnar structure formed by an oblique deposition method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Evaporation source 11 Discharge lamp 12 Elliptical condensing mirror 13 First plane mirror 14 Shutter 15 Integrator lens 16 Second plane mirror 17 Collimator lens 18 Filter 19 Polarizing element 20 Alignment microscope 21 Work stage M Mask W Work W

Claims (3)

[Claims] 1. A filter that polarizes light in a specific wavelength range formed by depositing a multilayer film on a substrate, wherein a refractive index of a light component incident on the filter with respect to a predetermined polarization component is equal to or less than that of the multilayer film. A polarizing filter characterized in that films of adjacent layers are different from each other. 2. The multilayer film according to claim 1, wherein a first film having a constant film thickness and a second film having a film thickness different from each other in a slope shape are alternately deposited, and the optical thickness of each film in a substantially central portion of the filter. 2 is formed so as to be ４ of the wavelength of the specific light, and the slope directions of two second films adjacent to the first film are exactly opposite to each other. Polarizing filter. 3. The polarizing filter according to claim 2, wherein the second film is formed by an oblique deposition method.