JP5867439B2 - Grid polarizing element and optical alignment apparatus - Google Patents

Description

  The present invention relates to a grid polarizing element.

  Various polarizing elements for obtaining polarized light are known as optical elements such as polarizing filters and polarizing films, as well as familiar products such as polarizing sunglasses, and are also widely used in display devices such as liquid crystal displays. Polarizing elements are classified into several types according to the method of extracting polarized light, and one of them is a grid polarizer.

  The grid polarizing element has a structure in which a fine striped lattice made of metal (conductor) is provided on a transparent substrate. It functions as a polarizer by making the interval of the grating narrower than the wavelength of light to be polarized. Of linearly polarized light, polarized light having an electric field component in the length direction of the grating is reflected because it is equivalent to a flat metal, whereas only polarized substrate is reflected for polarized light having an electric field component in a direction perpendicular to the length direction. Since it is equivalent to being, it is transmitted through the transparent substrate and emitted. For this reason, linearly polarized light in a direction perpendicular to the length direction of the grating is exclusively emitted from the polarizer. By controlling the orientation of the polarizing element so that the length direction of the grating is in a desired direction, polarized light in which the axis of the polarized light (direction of the electric field component) is directed in the desired direction can be obtained. .

  Hereinafter, for convenience of explanation, polarized light having an electric field component in the length direction of the grating is referred to as s-polarized light, and polarized light having an electric field component in a direction perpendicular to the length direction is referred to as p-polarized light. Usually, the surface that is perpendicular to the incident surface (the surface that is perpendicular to the reflecting surface and includes the incident light and the reflected light) is called the s wave, and the one that is parallel to the incident surface is called the p wave. The distinction is made on the assumption that they are parallel.

  The basic indicators for the performance of such a polarizing element are the extinction ratio ER and the transmittance TR. The extinction ratio ER is the ratio (Ip / Is) of the intensity (Ip) of p-polarized light to the intensity (Is) of s-polarized light among the intensity of polarized light transmitted through the polarizing element. Further, the transmittance TR is normally the energy of outgoing p-polarized light with respect to the total energy of incident s-polarized light and p-polarized light (TR = Ip / (Ip + Is)). An ideal polarizing element has an extinction ratio ER = ∞ and a transmittance TR = 50%.

JP 2011-8172 A

  Regarding the use of light, light in the visible range is often used as represented by display technology, but light in the infrared range is used in fields such as optical communication. On the other hand, light is often used as energy, and in this case, ultraviolet light is often used. For example, resist exposure (photosensitive processing) in photolithography, UV curing resin curing processing, and the like. Therefore, in the field of using polarized light, when using polarized light as energy, polarized light having a wavelength in the ultraviolet region is required.

  As a more specific example, in recent years, a technique called photo-alignment has been adopted in a liquid crystal display manufacturing process. This technique is a technique for obtaining an alignment film necessary for a liquid crystal display by light irradiation. When a film made of resin such as polyimide is irradiated with polarized light in the ultraviolet region, molecules in the film are aligned in the direction of the polarized light, and an alignment film is obtained. Compared to a mechanical alignment process called rubbing, a high-performance alignment film can be obtained, so that it has been widely adopted as a manufacturing process for high-quality liquid crystal displays.

  As described above, in certain types of applications, it is necessary to obtain polarized light in a shorter wavelength range, and a polarizing element for this purpose is required. However, such a polarizing element that polarizes light in the short wavelength region has not been studied so much, and practical products are hardly available. The short wavelength region is a wavelength region from the visible short wavelength side (for example, 450 nm or less) to the ultraviolet region.

For visible light, a polarizing film in which the absorption axis of the resin layer is aligned is often used. However, it cannot be used for ultraviolet rays because the resin deteriorates in a short time due to ultraviolet rays.
When polarizing light in the ultraviolet region, a prism polarizer using calcite can be used. However, the prism polarizer is suitable for an application of irradiating polarized light to a narrow area such as a laser, but is not suitable for an application of irradiating polarized light to a certain wide area such as photo-alignment.
The wire grid polarizing element described above can irradiate polarized light to a certain wide area. It is also possible to arrange a plurality of wire grid polarization elements and irradiate polarized light over a wider area.

  In the wire grid polarizing element, tungsten, copper, aluminum or the like is used as the material of the striped lattice. In the case of a wire grid polarizing element for ultraviolet rays, aluminum having a high reflectance in the ultraviolet region is often used. However, although the wire grid polarization element shows a certain high extinction ratio and transmittance for light in the visible range longer than about 500 nm, the extinction ratio and transmittance suddenly decrease from around 400 nm as the wavelength becomes shorter. . The reason for this is not fully understood, but is presumed to be due to the optical properties of aluminum.

As described above, in applications of optical processes such as photo-alignment, a practical polarizing element that can irradiate polarized light in the visible short wavelength region to the ultraviolet region to a wide area is desired, but the extinction ratio and transmittance A polarizing element excellent in basic performance has not been developed yet. That is, in order to improve the quality of the alignment treatment, it is necessary to irradiate only polarized light directed in a desired direction (improving the extinction ratio), and in order to increase productivity (treatment efficiency), A polarizing element having a high transmittance is required.
The invention of the present application has been made in view of such problems, and can irradiate polarized light in the visible short wavelength region to the ultraviolet region to a certain wide area, and has excellent characteristics in basic performance such as extinction ratio and transmittance. It is meaningful to provide a polarizing element having the following characteristics.

In order to solve the above-mentioned problem, the invention according to claim 1 of the present application is a grid polarizing element including a transparent substrate and a striped grating provided on the transparent substrate,
Each linear part constituting the grating is an amorphous titanium oxide film (excluding those in which k is 1.5 or more) where the refractive index real part n is larger than the extinction coefficient k at a wavelength of 240 nm or more and 400 nm or less. It consists of
The average value of the widths of the respective linear parts constituting the lattice is w, the distance between each linear part and the adjacent linear part on one side is t, and the distance between the adjacent linear part on the other side is T. Then, the lattice periodically has a portion where t <T, and in the portion where t <T, t / T> 0.0149w + 0.0644 (where t, T, The unit of w is a nanometer) .
In order to solve the above problem, the invention according to claim 2 is the configuration according to claim 1, wherein the lattice is in a direction along the surface of the transparent substrate and in the length direction of the linear portion. When viewed in the vertical direction, there is no portion where the portions where the two linear portions are arranged at a wide distance T are continuous.
In order to solve the above problems, the invention described in claim 3 includes a light source and the grid polarizing element described in claim 1 or 2, and the grid polarizing element is provided with a film material for photo-alignment. It is provided at a position between the irradiated region and the light source, and the light from the light source can be irradiated onto the photo-alignment film material through the grid polarizing element.

As described below, according to the first aspect of the present invention, the lattice is formed of amorphous titanium oxide, and the uneven distribution ratio t / T of the lattice with respect to the lattice width w is t / T> 0.0149w + 0. .0644, the extinction ratio can be improved without significantly reducing the transmittance. For this reason, it is possible to irradiate polarized light with better quality.
Further, according to the invention described in claim 2, in addition to the above effect, the extinction ratio may be lowered because the portion where the linear portions are arranged at a wide separation interval T does not exist. Absent.
Further, according to the invention described in claim 3, in addition to the above effects, photo-alignment can be performed while irradiating high-quality polarized light with high energy, so that a high-quality photo-alignment film can be obtained with high productivity. become.

It is the schematic which showed typically the grid polarizing element which concerns on embodiment of this invention, (1) is front sectional schematic, (2) is a perspective view. It is the schematic shown about the optical constant of the titanium oxide film produced in the experiment which inventors conducted. It is the figure shown about the optical constant of aluminum. FIG. 3 is a diagram showing a result of simulating a change in transmittance and extinction ratio with an uneven distribution ratio (t / T) in the grid element of the embodiment using the titanium oxide film showing the optical constant of FIG. 2. FIG. 3 is a diagram showing the result of simulating what the transmittance and extinction ratio will be when the uneven distribution ratio t / T is changed when aluminum having an optical constant shown in FIG. 3 is used as the material of the grating 2. It is the schematic perspective view shown about the reason which the extinction ratio improved in the grid polarizing element of embodiment. It is a figure which shows the result of the simulation which confirmed the wave of the x direction magnetic field component. It is the front section schematic diagram showing typically a mode that electric field Ey was newly generated by the wave (rotation) of magnetic field component Hx. It is the figure which showed the optical constant of the titanium oxide thin film formed into a film at 300 degreeC. FIG. 9 is a diagram showing a simulation result of the transmittance and the extinction ratio when the uneven distribution ratio t / T is similarly changed for the titanium oxide thin film having the optical constant in FIG. It is a figure of the result of having examined the optimal structure of the grid polarizing element using the grating | lattice 2 made from a titanium oxide. It is the figure shown about the optical constant of the titanium oxide of a rutile type crystal. It is a figure which shows the result of having simulated what a transmittance | permeability and an extinction ratio will be with respect to uneven distribution ratio t / T, when a rutile type titanium oxide is employ | adopted as a material of the grating | lattice 2. It is the schematic shown about the manufacturing method of the grid polarizing element of embodiment. It is an example of use of a grid polarization element of an embodiment, and is a section schematic diagram of an optical orientation device carrying a grid polarization element.

Next, modes (embodiments) for carrying out the present invention will be described.
FIG. 1 is a schematic diagram schematically showing a grid polarizing element according to an embodiment of the present invention, in which (1) is a schematic front sectional view and (2) is a perspective view. The grid polarizing element shown in FIG. 1 is mainly composed of a transparent substrate 1 made of a transparent material and a grating 2 provided on the transparent substrate 1. The polarizing element of the embodiment has a structure similar to a wire grid polarizing element. However, as will be described later, the grating 2 is not a conductor (wire), and is simply referred to as a grid polarizing element.

  The transparent substrate 1 is “transparent” in the sense that it has sufficient transparency with respect to the wavelength used (the wavelength of light polarized using a polarizing element). In this embodiment, since light in the ultraviolet region is assumed as a use wavelength, quartz glass (for example, synthetic quartz) is adopted as the material of the transparent substrate 1.

  As shown in FIG. 1, the lattice 2 has a stripe shape composed of a large number of linear portions 21 extending in parallel. Each linear portion 21 is formed of amorphous titanium oxide. The average value of the width of each linear portion 21 is w, the distance from the adjacent linear portion 21 on one side in each linear portion 21 is t, and the distance from the adjacent linear portion 21 on the other side is T. In this case, there is a portion where t <T is substantially periodic, and in the portion where t <T, the relationship is t / T> 0.0149w + 0.0644. Hereinafter, for convenience of explanation, t / T is referred to as uneven distribution ratio, and width w is abbreviated as lattice width.

In the above description, “substantially t <T” means that the separation distance t on one side is substantially different from the separation distance T on the other side. The term “substantially” means that the difference in distance that occurs due to manufacturing variations is not included, and that t ≠ T is intentionally set so that the action described later is exhibited.
Further, “periodic” means that it is not random. When t ≠ T is caused by manufacturing variation, it is random. However, t ≠ T is intentionally set so that the operation described later is exhibited, and therefore it is periodic. In this case, the term “periodic” means that t ≠ T is periodically present when viewed in a direction perpendicular to the length direction of the grating 2 along the surface of the transparent substrate 1. .

The configuration of the grid polarizing element according to such an embodiment is such that a higher extinction ratio and transmittance can be obtained in a region from the visible short wavelength region to the ultraviolet region (hereinafter collectively referred to as a short wavelength region). This is the result of inventors' diligent research on what it is like.
As a result of intensive studies on the structure and materials of the grid polarizing element, particularly the grating 2, which has an extinction ratio and transmittance in the short wavelength region, the inventors have found that the grating is based on a different concept from the conventional wire grid polarizing element. It has been found that it is effective to select the material and structure of 2.

  A conventional wire grid polarizing element can be called a reflective grid polarizing element. It uses a highly reflective metal for the grating 2 and is transparent by reflecting linearly polarized light having an electric field component in the length direction of the grating 2. This prevents the substrate 1 from being transmitted. In the grid polarizing element based on such a concept, as described above, there is a limit to improvement in basic performance such as extinction ratio and transmittance in a shorter wavelength region.

  The inventors of the present application have come up with a concept that should be called an absorption grid polarizing element, unlike the conventional grid polarizing element. The absorption type does not use absorption of light by a polymer as seen in a polarizing film for visible light or the like, but uses attenuation of light by an electromagnetic induction phenomenon.

式１において、ｎは複素屈折率の実部、ｋはいわゆる減衰係数である。発明者らが想到するに至った電磁誘導現象による光の減衰を利用したグリッド偏光素子は、減衰係数ｋに比べて屈折率実部ｎが大きく、不均等なグリッド構造を採用した場合に得られる。 As is well known, in the propagation of light in a conductive medium such as metal, the refractive index is treated as a complex refractive index. In order to distinguish the complex refractive index from the normal refractive index, when n ′, the complex refractive index n ′ is expressed by the following Equation 1.

In Equation 1, n is the real part of the complex refractive index, and k is a so-called attenuation coefficient. The grid polarization element using the attenuation of light due to the electromagnetic induction phenomenon that the inventors have conceived of is obtained when the real part n of the refractive index is larger than the attenuation coefficient k and an uneven grid structure is adopted. .

  First, the complex refractive index of titanium oxide used as a grating material in the grid polarizing element of the embodiment and the complex refractive index of aluminum as a comparative example will be described. FIG. 2 is a schematic view showing optical constants (refractive index real part n, extinction coefficient k) of a titanium oxide film created in an experiment conducted by the inventors. Figure 3 shows the optical constants of aluminum. Aleksandar D. Raki ?. Algorithm for the determination of intrinsic optical constants of metal films: application to aluminum, Appl. Opt. 34, 4755-4767 (1995) It was created based on the indicated data.

The titanium oxide film having the optical constant shown in FIG. 2 is formed on the quartz transparent substrate 1 by the ALD method described later, and the temperature at the time of film formation is about 100 ° C. Therefore, it is estimated that the state of the film is amorphous. The film thickness is about 20 nm. As shown in FIG. 2, the refractive index real part n is larger than the extinction coefficient k at a wavelength in the ultraviolet region of about 240 nm to 400 nm. On the other hand, as shown in FIG. 3, in the case of aluminum, the refractive index real part n is always smaller than the extinction coefficient k in the same short wavelength region.

  FIG. 4 is a diagram showing a result of simulating the propagation state of electromagnetic waves in the grid element of the embodiment. In FIG. 4, the case where the grid polarizing element shown in FIG. 1 is configured by the titanium oxide thin film shown in FIG. 2 is hypothesized, and the transmittance TR and the extinction ratio ER are changed when the uneven distribution ratio t / T is changed variously. It is simulated how it changes. In FIG. 4, (1) indicates the transmittance, and (2) indicates the extinction ratio. 2) The RCWA (Rigorous Coupled-Wave Analysis) method is used in the simulation of FIG. 2, and the software distributed by the National Institute of Standards and Technology (NIST) (http://physics.nist.gov/Divisions/ Div844 / facilities / scatmech / html / grating.htm) was used to calculate the transmittance TR and extinction ratio ER at each t / T.

As shown in FIG. 2, the real part n of the refractive index and the attenuation coefficient k have different values depending on the wavelength. As an example, it is assumed that 254 nm ultraviolet rays are used, and n and k at this wavelength are used. Specifically, n = 2.35 and k = 1.33. The dielectric constant was calculated and substituted in advance from n and k. Moreover, although the width w of the grating 2 was changed at intervals of 5 nm between 10 and 30 nm, the height was constant at 170 nm. In each lattice width w of 10 to 30 nm, the uneven distribution ratio t / T was changed. Note that t / T was changed by increasing t and decreasing T so as to always satisfy t + T = 180 nm, starting from t = T = 90 nm when the uneven distribution ratio t / T = 1. .

In FIG. 4 (1), the transmittance when t / T = 1 (when not unevenly distributed) is 1, and the transmittance when t / T is less than 1 is shown as a relative value. Yes. The extinction ratio in FIG. 4 (2) is the same, and is shown as a relative value when the value when t / T = 1 is 1.
As shown in FIG. 4 (1), the transmittance is slightly reduced when it is less than 1 as compared with the case of t / T = 1, but does not show a significant decrease with the grating width w of 10 to 20 nm. Even with a lattice width of 20 to 30 nm, there is no significant decrease in transmittance as long as t / T = 1 to 0.7.
On the other hand, as shown in FIG. 4 (2), it is confirmed that the extinction ratio is improved by setting t / T to less than 1 compared to the case of t / T = 1. In particular, a significant improvement is confirmed when the grating width w is 15 to 25 nm.

  Next, as a comparative example, the result of a similar simulation for the case where aluminum shown in FIG. FIG. 5 is a diagram showing the results of simulating what the transmittance and extinction ratio would be if the uneven distribution ratio t / T was changed when aluminum having the optical constant shown in FIG. is there. Similarly, FIG. 5A shows the transmittance TR, and FIG. 5B shows the extinction ratio ER. Similarly, the wavelength used is assumed to be 254 nm, and the refractive index real part n = 0.183 and the extinction coefficient k = 2.93 are assumed to be obtained at this wavelength. Similarly, the width of the grating 2 was changed from 10 to 30 nm in increments of 5 nm, and the height was constant at 170 nm.

As shown in FIG. 5A, in the case of the grating 2 made of aluminum, it is confirmed that the transmittance TR is slightly improved in the grating width W of 10 to 20 nm. The transmittance TR is higher when the uneven distribution ratio t / T is smaller, and is about 40% at the maximum. However, as shown in FIG. 5 (2), the extinction ratio decreases drastically when t / T is made smaller than 1 for any lattice width w . The reduction in the extinction ratio is significant in a region where the uneven distribution ratio t / T is small in which the improvement in transmittance is partially confirmed. That is, in the case of the grating 2 made of aluminum, it was confirmed that even if the grating 2 is unevenly distributed, the essential extinction ratio is lowered, and improvement in transmittance and improvement in the extinction ratio are not compatible. Although illustration is omitted, it is confirmed that aluminum is the same when the wavelength is 365 nm, and the extinction ratio is not only improved but is drastically reduced even if the uneven distribution ratio t / T is less than 1.

  As described above, in the case of a conventional grid polarizing element of an aluminum grid 2, the extinction ratio is not improved even if the grid 2 is unevenly distributed, whereas the grid 2 made of titanium oxide is used. In the grid polarizing element of the embodiment described above, the structure in which the grating 2 is unevenly distributed under a certain condition can greatly improve the extinction ratio, and in that case, the transmittance is not greatly reduced.

The reason why the extinction ratio can be improved in the grid polarizing element of the embodiment having the lattice 2 made of titanium oxide will be described below. FIG. 6 is a schematic perspective view schematically showing the reason why the extinction ratio is improved in the grid polarizing element of the embodiment.
As described above, the extinction ratio is the ratio of the intensity (Ip) of the p-polarized light to the intensity (Is) of the s-polarized light. Therefore, in order to increase the extinction ratio, the s-polarized light cannot pass through the polarizing element. Here, the behavior of s-polarized light is mainly considered here.

In FIG. 6, for the sake of convenience, it is assumed that light propagates from the top to the bottom on the paper surface, and this direction is the z direction. Further, the direction in which the grating 2 extends is the y direction, and therefore the s-polarized light (indicated by Ls in FIG. 6) has an electric field component Ey. The magnetic field component (not shown) of this s-polarized light is in the x direction (Hx).
When such s-polarized light reaches the grid 2 of the grid polarization element, the electric field Ey of the s-polarized light is weakened by the dielectric constant of the grid 2. On the other hand, the medium between the gratings 2 is often air, but generally the dielectric constant is smaller than that of the grating 2, so the electric field Ey is not weakened as much as in the grating 2 in the space between the gratings 2.

即ち、格子２間の中央の電界Ｅｙの最も高いところを境に、一方の側ではＨｚは光の伝搬方向前方に向き、他方の側ではＨｚは後方を向く。ここで、図６では省略されているが、ｘ方向の磁界ＨｘはＥｙと同位相で、ｘ軸負の側を向いて存在している。このｘ方向磁界成分Ｈｘは、生成されたｚ方向成分Ｈｚに引っ張られ、波打つように変形する。 As a result, a rotation component of the electric field Ey is generated in the xy plane. Then, the following Maxwell equation (Formula 2) corresponding to Faraday's electromagnetic induction induces a magnetic field Hz in two z directions opposite to each other in accordance with the strength of the rotation Re in the xy plane. The

That is, with the highest electric field Ey at the center between the gratings 2 as a boundary, Hz is directed forward in the light propagation direction on one side, and Hz is directed backward on the other side. Here, although omitted in FIG. 6, the magnetic field Hx in the x direction has the same phase as Ey and exists toward the negative side of the x axis. The x-direction magnetic field component Hx is pulled by the generated z-direction component Hz and deforms so as to wave.

  FIG. 7 is a diagram showing the result of a simulation confirming the undulation of the x-direction magnetic field component Hx. FIG. 7 shows an example of simulation using silicon as the lattice material. Silicon, for example, is an ultraviolet ray having a wavelength of 365 nm, a refractive index real part n = 4.03, an extinction coefficient of 3.04, and n> k. In FIG. 7, the width of the linear portions is 15 nm, the interval between the linear portions is constant at 90 nm, and the height of each linear portion is 170 nm. The simulation was based on the FDTD (Finite-Difference Time-Domain) method, and the software used was MATLAB (registered trademark) of Mathworks (Massachusetts, USA).

In FIG. 7, the dark black portion on the upper side indicates the negative component of the electric field Ez, and the light gray portion in the middle indicates the positive component of the electric field Ez. The magnetic field is indicated by a vector (arrow).
As shown in FIG. 7, the s-polarized light before reaching the grating 2 has only the Hx component because there is no Hz component, but the generation of the above-mentioned Hz component reaching the grating 2 causes the magnetic field to be in the xy plane. It can be confirmed that it undulates. As shown in FIG. 7, the undulation of the magnetic field is a situation that can be said to be a clockwise rotation of the magnetic field. In FIG. 7, the y direction is the light propagation direction, and the z direction is the length direction of the grating 2, which is different from FIG. 6.

この様子を図８において模式的に示す。図８は、磁界成分Ｈｘの波打ち（回転）により新たに電界Ｅｙが発生する様子を模式的に示した正面断面概略図である。 When such undulation (rotation) of the magnetic field component Hz occurs, an electric field is further generated in the y direction by the Maxwell equation (Equation 3) corresponding to Ampere Maxwell's law.

This is schematically shown in FIG. FIG. 8 is a schematic front cross-sectional view schematically showing a state in which an electric field Ey is newly generated by undulation (rotation) of the magnetic field component Hx.

  As shown in FIG. 8, due to the undulation (rotation) of the magnetic field component Hx in the xz plane, an electric field Ey directed toward the front side of FIG. In FIG. 3, an electric field Ey directed toward the back side of the paper is generated. In this case, since the original electric field Ey of the incident s-polarized light is directed toward the front side of the drawing, the electric field between the gratings 2 is canceled by the rotation of the magnetic field, and acts so that the wave is divided. As a result, the electric field Ey is localized in the grating 2, and the energy of the s-polarized light disappears while propagating through the grating 2 due to absorption according to the material of the grating 2.

  On the other hand, for p-polarized light, the electric field component is oriented in the x direction (Ex), but when viewed in the y direction, the dielectric constant distribution is uniform, so the electric field rotation component as described above is substantially Does not occur. Therefore, localization of the electric field such as s-polarized light in the grating 2 and attenuation in the grating 2 do not occur in the p-polarized light. That is, in this embodiment, the electric field Ey is localized in the grating 2 by generating a wave (rotation) of the magnetic field component Hx, and the s-polarized light is selectively attenuated by absorption in the grating 2. This is the principle of operation of the grid polarizing element. Such localization of the electric field Ey can be efficiently achieved by making the lattice 2 unevenly distributed and partially narrowing the interval between the lattices 2, thereby presuming that the extinction ratio can be increased. . The improvement of the extinction ratio shown in FIG. 4 is considered to be due to such a mechanism.

式４から、ｎ＜ｋということは、負の誘電率を持つということになる。このことは、波動が内部に入っていけないことを意味し、上記の場合には格子２内に電界が形成されないことを意味する。従って、上記のような電界の局在化は実質的に生じない。その一方、格子２を偏在化させることで格子間隔が広い場所が生じると、ｓ偏光光がその場所を通り抜けるようにして伝搬し易くなり、結果的に消光比が大きく低下してしまう。図５に示す消光比の激減は、このような状況を示しているものと推測される。 Further, the localization of the electric field Ey as described above does not substantially occur when the refractive index real part n is smaller than the extinction coefficient k as in aluminum. The real part n of the refractive index and the extinction coefficient k are expressed by the following formula 4 using the physical constants ε and μ.

From Equation 4, n <k means a negative dielectric constant. This means that waves cannot enter the inside, and in the above case, no electric field is formed in the lattice 2. Therefore, the localization of the electric field as described above does not substantially occur. On the other hand, when a place with a wide lattice interval is generated by making the grating 2 unevenly distributed, the s-polarized light easily propagates through the place, and as a result, the extinction ratio is greatly reduced. The drastic decrease in the extinction ratio shown in FIG. 5 is presumed to indicate such a situation.

Next, a more preferable structure of the grid polarizing element of the embodiment will be described.
First, the simulation result shown in FIG. 4 was based on the data of the titanium oxide thin film prepared at 100 ° C. shown in FIG. The inventors similarly made a titanium oxide thin film at a temperature of 300 ° C. and performed a simulation. FIG. 9 shows the optical constant of the titanium oxide thin film formed at 300 ° C., and FIG. 10 shows the case where the uneven distribution ratio t / T is changed for the titanium oxide thin film having the optical constant shown in FIG. It is the figure which showed the result of having simulated about the transmittance | permeability and extinction ratio.

As shown in FIG. 9, even in the case of forming a film at 300 ° C., the refractive index real part n is larger than the extinction coefficient k in the wavelength range of about 240 to 400 nm. Further, as shown in FIG. 10 (1), the transmittance does not decrease so much at a lattice width w of 10 to 20 nm, and the uneven distribution ratio t / T is 1 to 0.7 even at a lattice width w of 20 to 30 nm. In the range, the transmittance does not show a significant decrease. As shown in FIG. 10 (2), the extinction ratio is greatly improved in the lattice width excluding 10 nm.

  FIG. 11 is a diagram showing a result of examining an optimum structure of a grid polarizing element using such a titanium oxide lattice 2. As shown in FIG. 4 (2) and FIG. 10 (2), when the uneven distribution ratio t / T is decreased from 1 (distributed), in most cases, the extinction ratio immediately improves. . The extinction ratio peaks at a certain t / T, and then decreases. The extinction ratio becomes smaller than a relative value 1 at a certain t / T. That is, the extinction ratio is smaller than that in the case where the uneven distribution is not performed. Therefore, it is only necessary that the ratio of the eccentricity is equal to or greater than the value of t / T when the extinction ratio is below the relative value 1 (hereinafter referred to as the critical uneven ratio).

  FIG. 11 is a plot of this critical uneven distribution ratio. When the marker is film formation at 100 ° C. shown in FIG. 4 (2), the marker is when film formation at 300 ° C. shown in FIG. 10 (2). The straight line shown in FIG. 11 is a straight line drawn by applying the least square method for each marker. As shown here, in the case of film formation at 100 ° C., if t / T> 0.0147w−0.1134, the extinction ratio can be improved. In the case of film formation at 300 ° C., if t / T> 0.0149w + 0.0644, the extinction ratio can be improved.

  The titanium oxide thin film is often formed by CVD (chemical vapor deposition) such as ALD described later, and the film forming temperature is generally about 100 to 300 ° C. At temperatures below 100 ° C., it is difficult to obtain a film that can withstand practical use. In addition, when the film is formed at a temperature exceeding 300 ° C., the degree of crystallization advances and the amorphous state is often lost. Even when the film is formed at 300 ° C., if t / T> 0.0149w + 0.0644, the improvement of the extinction ratio can be expected. Therefore, if t / T> 0.0149w + 0.0644, the amorphous state is obtained. The effect of improving the extinction ratio can be expected for all grid polarizing elements including the grating 2 made of a titanium oxide thin film.

  Referring to avoiding the decrease in the transmittance, in FIG. 4A, the condition that the transmittance is decreased by, for example, 10% or more is the case where the grating width is 25 nm or more and t / T is smaller than about 0.4. . In FIG. 10A, the condition that the transmittance is reduced by 10% or more is that the lattice width is 25 nm or more and t / T is smaller than about 0.4. When this condition is applied to the graph of FIG. 11, it is confirmed that it is below the straight line of t / T = 0.0149w + 0.0644. In other words, if t / T> 0.0149w + 0.0644, it can be expected that the extinction ratio can be improved without greatly reducing the transmittance regardless of the grating width.

  Next, the case where the crystallized titanium oxide is employ | adopted as a material of the grating | lattice 2 as a comparative example is demonstrated. FIG. 12 is a diagram showing an optical constant of rutile-type titanium oxide as an example. This titanium oxide thin film is formed by CVD and then heat-treated at about 600 ° C. for crystallization. As shown in FIG. 12, in the case of rutile-type titanium oxide, n and k are reversed around 280 nm, and n> k at wavelengths longer than around 280 nm.

FIG. 13 is a diagram showing a result of simulating the transmittance and extinction ratio with respect to the uneven distribution ratio t / T when such rutile crystal titanium oxide is adopted as the material of the lattice 2. is there. In this simulation, the simulation was performed by the RCWA method on the assumption that the wavelength used was 254 nm and n = 1.55 and k = 3.09 obtained at this wavelength.
As shown in FIG. 13, in the case of rutile-type titanium oxide, although the transmittance is partially improved, the extinction ratio is drastically decreased at any uneven distribution ratio t / T. It can be seen that the effect of improving the extinction ratio by making T less than 1 cannot be obtained at all. That is, in order to improve the extinction ratio, it is important that the state of titanium oxide is amorphous.

In the case of a rutile type crystal, it is not always clear whether the reason why the effect of improving the extinction ratio cannot be obtained as described above is not because of the relationship of n> k or because it is not amorphous. It is speculated that both are the cause. In any case, the effect of improving the extinction ratio by optimizing the uneven distribution ratio t / T is possible when a lattice that is n> k and is amorphous is employed.
In addition, although the meanings of the terms “amorphous” and “crystal” are physically clear, in an actual grid polarization element, there are cases where the amorphous structure and the crystal structure part are mixed in the lattice structure. is there. In such a case, if it has an amorphous structure in a region more than half of the lattice, it can be said to be “amorphous”. For the evaluation of crystallinity, an X-ray diffraction method, Rutherford backscattering analysis (RBS), or the like is used. If the peak is less than half of the peak showing a complete crystal state in such an analysis, it is amorphous. It can be assumed that Note that the crystalline state includes so-called microcrystals.

Next, the manufacturing method of the grid polarizing element of the said embodiment is demonstrated.
FIG. 14 is a schematic view illustrating a method for manufacturing the grid polarizing element of the embodiment. In the manufacturing method according to the embodiment, first, the intermediate thin film 3 is formed on the transparent substrate 1 as shown in FIG. The intermediate thin film 3 is a thin film that serves as a base for forming a thin film for a lattice. Since the intermediate thin film 3 is finally removed, the material is not particularly limited. It is sufficient that the shape stability is good and that it can be quickly removed during etching. For example, an organic material such as a photoresist, silicon, carbon, or the like is selected as the material for the intermediate thin film 3.

  Next, as shown in FIG. 14B, the intermediate thin film 3 is patterned by photolithography. That is, the intermediate thin film is patterned by coating the entire surface of the photoresist, exposing, developing, and etching. The patterning is performed so that the intermediate thin film 3 has a stripe shape extending in the direction perpendicular to the paper surface. At this time, the width L1 and the interval L2 of the stripes of the intermediate thin film 3 determine the intervals t and T of the lattice 2 to be finally produced.

  Next, as shown in FIG. 14 (3), the lattice thin film 4 is formed so as to cover the entire surface of the patterned intermediate thin film 3. The lattice thin film 4 is a thin film made of a lattice material, that is, titanium oxide. The lattice thin film 4 is formed by ALD (Atomic Layer Deposition) which is a kind of thermal CVD. ALD is a technique in which precursor gas phase molecules are supplied little by little onto a substrate placed in a reaction vessel, and are adsorbed and formed into a single atomic layer. After the precursor reaction is saturated, the gas phase molecules are purged and the precursor gas phase molecules are supplied again. By repeating this, a thin film having a predetermined thickness is formed. In some cases, a plasma pulse is applied in order to reduce the deposition temperature or increase the deposition rate.

After forming the lattice thin film 4 in this manner, the lattice thin film 4 is anisotropically etched. Anisotropic etching is etching in the thickness direction of the transparent substrate 1. By this etching, as shown in FIG. 14 (4), the lattice thin film 4 remains on both side walls of the pattern of the intermediate thin film 3. Thereafter, etching is performed using an etchant that can etch only the material of the intermediate thin film 3, and the entire pattern of the intermediate thin film 3 is removed. As a result, the grid 2 composed of the respective linear portions 21 made of titanium oxide is formed on the transparent substrate 1, and the grid polarizing element of the embodiment is obtained. The obtained grid polarization element has a predetermined uneven distribution ratio t / T, and the pattern dimensions L1 and L2 of the intermediate thin film 3 are determined according to the lattice width w so as to have this value.

Next, a usage example of such a grid polarizing element will be described. FIG. 15 shows an example of use of the grid polarizing element of the embodiment, and is a schematic sectional view of a photo-alignment apparatus equipped with the grid polarizing element.
The apparatus shown in FIG. 15 is a photo-alignment apparatus for obtaining the above-described photo-alignment film for a liquid crystal display. By irradiating the object (work) 10 with polarized light, the molecular structure of the work 10 is in a certain direction. It will be in a state of being aligned. Accordingly, the workpiece 10 is a film (film material) for a photo-alignment film, and is, for example, a polyimide sheet. When the workpiece 10 has a sheet shape, a roll-to-roll conveyance method is adopted, and polarized light is irradiated during the conveyance. A liquid crystal substrate covered with a film material for photo-alignment may be a workpiece. In this case, a configuration in which the liquid crystal substrate is transported on a stage or transported by a conveyor is employed.

The apparatus shown in FIG. 15 includes a light source 5, a mirror 6 that covers the back of the light source 5, and a grid polarizing element 7 disposed between the light source 5 and the workpiece 6. The grid polarizing element 7 is that of the above-described embodiment.
In many cases, ultraviolet light irradiation is required for photo-alignment, and therefore, an ultraviolet lamp such as a high-pressure mercury lamp is used as the light source 5. The light source 5 is long in the direction perpendicular to the conveying direction of the workpiece 10 (here, the direction perpendicular to the paper surface).

As described above, the grid polarizing element 7 selectively transmits p-polarized light based on the length of the grating 2. Therefore, the grid polarizing element 7 is arranged with high posture accuracy with respect to the work 10 so that the polarization axis of the p-polarized light is directed in the direction in which the optical alignment is performed.
In addition, since it is difficult to manufacture a large-sized grid polarizing element, when it is necessary to irradiate a large area with polarized light, a configuration in which a plurality of grid polarizing elements are arranged on the same plane is adopted. In this case, the surface on which the plurality of grid polarization elements are arranged is parallel to the surface of the work 10, and each grid polarization element is arranged so that the length direction of the grating in each grid polarization element is a predetermined direction with respect to the work. Be placed.

According to the grid polarizing element of the embodiment described above, the lattice 2 is formed of amorphous titanium oxide, and the uneven distribution ratio t / T of the lattice 2 with respect to the lattice width w is t / T> 0.0149w + 0.0644. Therefore, the extinction ratio can be improved without significantly reducing the transmittance. For this reason, it is possible to irradiate polarized light with better quality. In addition, when the lattice width w is different for each linear portion 21 due to manufacturing variations and other reasons, the average value of the widths of the linear portions 21 is applied when applying to the above formula.
And since the optical alignment apparatus equipped with such a grid polarizing element uses a grid polarizing element with a high extinction ratio, it becomes possible to perform a high-quality optical alignment process, and a high-quality optical alignment film is formed. Can be obtained. This can greatly contribute to the production of high-quality displays.

In the structure of the grid polarizing element of the embodiment, it has been described that the portion where t ≠ T periodically exists. However, the structure where the portion of the distance t and the portion of the distance T exist alternately (see FIG. The structure shown in FIG. 1 is an example. Many other periodic lattice uneven structures can be considered. However, it is not preferable that the portions where the linear portions 21 are arranged at a wide separation interval T are continuous. This is because p-polarized light is easily transmitted through the portion, and the extinction ratio is lowered. When the lattice spacing pattern is represented by t (narrow) and T (wide), other preferable examples include ttTttTttT ..., ttTtTttTtT ..., and the like. Including this example, the present invention does not exclude including a portion where t = T. That is, it is not an essential requirement that t ≠ T at all locations. However, from the viewpoint of obtaining an effect of improving the extinction ratio, it is preferable that t ≠ T in more than half of the entire region of the lattice.
Moreover, although the wavelength range which can use the grid polarizing element of this invention suitably is the short wavelength side and the ultraviolet region in the visible region, it may be used exclusively in the ultraviolet region.

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Grating 21 Linear part 3 Intermediate thin film 4 Lattice thin film 5 Light source 6 Mirror 7 Grid polarization element 10 Workpiece

Claims (3)

A grid polarizing element comprising a transparent substrate and a striped grating provided on the transparent substrate,
Each linear part constituting the grating is an amorphous titanium oxide film (excluding those in which k is 1.5 or more) where the refractive index real part n is larger than the extinction coefficient k at a wavelength of 240 nm or more and 400 nm or less. It consists of
The average value of the widths of the respective linear parts constituting the lattice is w, the distance between each linear part and the adjacent linear part on one side is t, and the distance between the adjacent linear part on the other side is T. Then, the lattice periodically has a portion where t <T, and in the portion where t <T, t / T> 0.0149w + 0.0644 (where t, T, The grid polarizing element is characterized in that the unit of w is nanometer) .    The lattice is a portion in which two linear portions are arranged at a wide distance T when viewed in a direction along the surface of the transparent substrate and perpendicular to the length direction of the linear portions. The grid polarizing element according to claim 1, wherein the grid polarizing element does not have a continuous portion.   A grid polarization element according to claim 1 or 2 is provided, and the grid polarization element is provided at a position between the light source and an irradiation region where a film material for photo-alignment is disposed. A photo-alignment apparatus characterized in that light from the light source can be applied to a photo-alignment film material through the grid polarizing element.

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