JP6940928B2 - Depolarization element and its manufacturing method, and optical equipment and liquid crystal display device using it. - Google Patents

Description

The present invention relates to a depolarizing element capable of eliminating the polarized state when light in a predetermined polarized state is incident, a method for manufacturing the same, and an optical device and a liquid crystal display device using the same.

When optical instruments such as spectroscopes, amplifiers, and measuring instruments have polarization dependence, if the light incident on these optical instruments is in a predetermined polarization state, the output decreases, the reflection characteristics change, etc. due to the polarization dependence, and the optics The function of the device cannot be fully fulfilled. For example, in a single focus projector or the like, since the reflection characteristics of the screen differ depending on the polarization state of the projected light, uneven brightness and uneven color occur on the projected screen. Therefore, a depolarizing element capable of eliminating a polarized state before light is incident on an optical device having a polarization dependence is used.

In the conventional depolarization element, a Babine-type depolarization element has been used in which the thickness of the birefringent crystal is changed in the incident plane, thereby changing the amount of retardation in the plane. When a depolarizing element is manufactured using a birefringent crystal, the size that can be manufactured depends on the crystal size. Further, if there is a change in the thickness of the birefringent layer, it is inevitable that the direction of the incident light will change due to the refraction of the light.

Therefore, as a depolarizing element, a plurality of sub-wavelength structure regions having optical characteristics different from those of the substrate are formed on the surface of the substrate, and the incident light is converted into a polarization state corresponding to each periodic structure to eliminate the polarization. Has been considered.

For example, in Patent Document 1, a plurality of structures exhibiting structural birefringence by alternately providing two types of media having different refractive indexes in a striped shape at a period shorter than the wavelength of light on the surface layer portion of the substrate. A depolarizing element has been proposed in which the optical axes are arranged in a plane so as to face different directions in the same plane. According to Patent Document 1, by using this depolarizing element, even if the incident light is polarized in a specific direction, the incident light passes through each structure, so that the emitted light is emitted from each structure. Polarized light is mixed in different directions according to the direction of the optical axis, and as a result, the polarized light is eliminated.

Further, in Patent Document 2, a plurality of sub-wavelength structure regions having structural birefringence are arranged adjacent to each other on the surface layer portion of the substrate, and the sub-wavelength structure region is the light used. It has grooves that are repeatedly arranged in a cycle shorter than the wavelength, and is arranged so that the optical axis direction, which is the arrangement direction of the grooves, has different portions between adjacent sub-wavelength structure regions, and the polarized light is used. As the elimination element, a polarization elimination element including a groove having a different depth has been proposed. The depolarizing element of Patent Document 2 changes the retardation by changing the depth of the groove, and changes the polarization of the emitted light for each position of the substrate to eliminate the polarization.

Japanese Unexamined Patent Publication No. 2004-341453 Japanese Unexamined Patent Publication No. 2011-180581

In the depolarizing plate described in Patent Document 1, a plurality of structures provided in a stripe shape so that the optical axes face in different directions in the same plane are arranged, and each structure serves as a divided region. It is considered that it cannot be sufficiently resolved. In addition, if an attempt is made to reduce the divided region (structure) in order to eliminate polarized light more reliably, pattern formation becomes difficult, and even if each structure is randomly arranged, a certain degree of regularity remains, which is a limit. There is. Further, in the depolarizing plate described in Patent Document 1, since the divided region is formed by linear lines, there is a concern that diffracted light may be generated depending on the pitch of the lines and adversely affect the optical characteristics. Further, when such a depolarizing plate is used in a liquid crystal display device, moire and diffraction may occur, which may lead to deterioration of image quality.

Further, in order to produce the depolarizing element including the groove described in Patent Document 2, a flat film having a high refractive index is first deposited on the substrate by a sputtering method or the like, and then the division pattern is formed by patterning by photolithography. It is necessary to perform the formation and finally the etching. At this time, a complicated process is required to make the groove depth different, pattern formation is difficult, and there is a concern that the cost will increase and the yield will deteriorate. Further, due to the difficulty of such a manufacturing process, it is assumed that the polarized light of the incident light cannot be sufficiently depolarized in the optical axis direction and the groove depth due to the groove of the depolarizing element actually manufactured.

Therefore, an object of the present invention is to provide a depolarization element which can be manufactured relatively easily as compared with a conventional depolarization element and which can surely depolarize the depolarized element and a method for manufacturing the depolarizing element. Another object of the present invention is to provide an optical device and a liquid crystal display device using this depolarizing element.

The present inventor has made diligent studies to achieve the above-mentioned objects. Here, the sub-wavelength structure having a periodic structure shorter than the wavelength of the light to be used (that is, the incident light) is a one-dimensional lattice structure having a (n _H > n _{L ) repeating structure with refractive indexes n H} and n _L. In this case, where f is the duty ratio, the effective refractive indexes of the TE wave and the TM wave are given by the following equations (1) and (2), respectively, and the magnitude of birefringence Δn (generally Δn = n _TE −n _TM) . There is also.) The following equations (1) and (2) are approximate equations that hold when the pitch is smaller than the wavelength of the incident light.

The polarization conversion by this structure depends on the retardation (optical path length difference) Re. The retardation Re is represented by the following equation (3) when the thickness d of the birefringent portion (that is, the periodic structure) is used.

Therefore, instead of changing the polarization according to the optical axis and the groove depth as proposed in Patent Documents 1 and 2, the duty ratio f due to the grid structure arranged at the pitch width equal to or less than the wavelength of the incident light is set. The inventor paid attention. Then, it was found that the retardation of the depolarizing element can be changed over the entire substrate surface by continuously changing the duty ratio of the grid structure along the axial direction of the grid structure. Further, it has been found that such a depolarizing element can be manufactured relatively easily as compared with a conventional depolarizing element, and depolarization can be reliably performed, and the present invention has been completed. ..

The present invention is based on the above-mentioned findings by the present inventor, and the means for solving the above-mentioned problems are as follows. That is,
<1> With a translucent substrate
It has a birefringent layer having a grid structure provided on the translucent substrate and arranged at a pitch width equal to or less than the wavelength of incident light.
The depolarizing element is characterized in that the duty ratio of the grid structure changes continuously along the axial direction of the grid structure.
The depolarizing element according to <1> can be manufactured relatively more easily than the conventional depolarizing element because the duty ratio of the grid structure changes continuously along the axial direction of the grid structure. Moreover, it is possible to provide a depolarizing element capable of reliably depolarizing the polarization.

<2> The depolarizing element according to <1>, wherein the duty ratio changes within a range of 0.2 or more and 0.6 or less.

<3> The depolarizing element according to <1> or <2>, wherein the input pitch width is less than 200 nm.

<4> The depolarizing element according to any one of <1> to <3>, wherein the height of the grid structure is constant.

<5> The depolarizing element according to any one of <1> to <4>, wherein the retardation of the birefringent layer continuously changes in the plane of the translucent substrate.

<6> The depolarizing element according to any one of <1> to <5>, wherein the birefringent layer is made of only an inorganic material.

<7> The depolarizing element according to any one of <1> to <6>, wherein the birefringent layer is covered with a protective film.

<8> The depolarizing element according to any one of <1> to <7>, wherein the pitch width is constant.

<9> The depolarizing element according to any one of <1> to <8>, wherein the duty ratio of the grid structure changes substantially periodically with respect to the axial direction.

<10> The method for manufacturing the depolarizing element according to any one of <1> to <9>.
This is a method for manufacturing a depolarizing element, characterized in that the grid structure is formed by using a two-luminous flux interference exposure method.
According to the manufacturing method according to <10>, it is possible to provide a method capable of easily manufacturing the depolarizing element according to any one of <1> to <9>.

<11> An optical device characterized in that the depolarizing element according to any one of <1> to <9> is mounted.
According to the optical device according to <11>, it is possible to provide an optical device having excellent optical characteristics.

<12> A liquid crystal display device comprising the depolarizing element according to any one of <1> to <9>.
According to the liquid crystal display device according to <12>, it is possible to provide a liquid crystal display device having excellent display characteristics.

According to the present invention, the above-mentioned problems in the prior art can be solved, the above object can be achieved, the fabrication can be performed relatively easily as compared with the conventional depolarization element, and the depolarization can be reliably performed. A depolarizing element and a method for manufacturing the same can be provided. Further, it is possible to provide an optical device and a liquid crystal display device using this depolarizing element.

It is a schematic diagram of the depolarizing element 100 according to one embodiment of the present invention, (A) is a top view, (B) is a cross-sectional view taken along the line II, and (C) is a cross-sectional view taken along the line II-II. be. It is a graph for demonstrating the polarization elimination element 100 according to one Embodiment of this invention, (A) shows an example of the change of the effective refractive index with respect to the duty ratio, (B) is the change of retardation with respect to the change of duty ratio. An example is shown. It is a schematic diagram of the depolarizing element 200 according to the preferred embodiment of the present invention, (A) is a schematic diagram at a position where the grid width W is the minimum, and (B) is a schematic diagram at a position where the grid width W is the maximum. .. It is a flowchart which shows the manufacturing method of the depolarizing plate according to one Embodiment of this invention.

Hereinafter, the present invention will be specifically described with reference to the drawings. Note that, for convenience of explanation, FIGS. 1, 3 and 4 exaggerate the sizes of the actual configurations. In principle, the same components are given the same reference numbers, and the description thereof will be omitted.

(Depolarization element)
A depolarizing element according to the present invention has a translucent substrate and a birefringent layer, and further includes other configurations, if necessary.

<Polarizing element>
Hereinafter, the depolarizing element 100 according to the embodiment of the present invention will be described with reference to FIG. The depolarizing element 100 according to an embodiment of the present invention is a birefringent layer 20 composed of a translucent substrate 10 and a grid structure provided on the translucent substrate 10 and arranged with a pitch width P equal to or less than the wavelength of incident light. And, and further include other configurations as needed. The present embodiment is characterized in that the duty ratio of the grid structure continuously changes along the axial direction of the grid structure (hereinafter, may be abbreviated as "grid axial direction").

Here, as shown in FIGS. 1A to 1C, the pitch width P is the sum of the grid width W of the grid structure and the gap width G between adjacent grids in the cross section of the grid axis. , P = W + G. The ratio (W / P) of the grid width W to the pitch width P is called a duty ratio (hereinafter referred to as duty ratio), and duty ratio = W / P = W / (W + G). Note that FIG. 1B is a cross-sectional view taken along the line I-I of FIG. 1A, which is a schematic cross-sectional view when the grid width W is the minimum W _min and the gap width G is the maximum G _max . be. On the other hand, FIG. 1C is a sectional view taken along line II-II of FIG. 1A, which is a schematic cross-sectional view when the grid width W is the maximum W _max and the gap width G is the minimum G _min . be. 1 (A) to 1 (C) are schematic views when the pitch width P is constant.

<< Translucent substrate >>
The translucent substrate 10 is not particularly limited as long as it is a material capable of transmitting light that eliminates the polarized state, and can be appropriately selected depending on the intended purpose. Examples of the material of such a translucent substrate include glass such as quartz glass, borosilicate glass, white plate glass, and float glass; and oxide crystals such as quartz and sapphire. Silicon can also be used for applications other than visible light.

<< Birefringence layer >>
The birefringent layer 20 is a layer provided on the translucent substrate 10, and as shown in FIG. 1, the duty ratio of the grid structure changes continuously along the grid axis direction. In the grid structure shown in FIG. 1 (A), a pitch width P in which a region surrounded by two sine waves line-symmetrical in the periodic direction (hereinafter, each of the grids in the cross-sectional view is referred to as a "unit region") is constant. It is arranged in parallel with. The pitch width P of the grid is set to be equal to or less than the wavelength of the incident light so that birefringence occurs. With this configuration, the duty ratio is not constant in the light passing region to be depolarized, and as a result, the retardation due to structural birefringence is not constant, and the polarized state of the transmitted light can be eliminated. Then, the retardation of the birefringent layer 20 changes continuously in the plane of the translucent substrate 10.

The grid structure according to this embodiment is not limited to the illustrated shape. As long as the duty ratio of the grid structure changes continuously along the grid axis direction, other shapes may be used, the pitch width P may be constant, may be gradually increased, or may be gradually decreased. It may change periodically. Further, the mode in which the duty ratio changes is not limited to the trigonometric change of the grid width W of the unit region shown as an example. For example, even in the case of a combination of a plurality of rhombuses in which unit regions are periodically connected, the duty ratio changes continuously along the axial direction of the grid structure. The term "continuous" as used herein includes, of course, a strict "continuous" in the mathematical sense, but it may be broadly considered as long as the effects of the present invention can be obtained. For example, as long as the effect of the present invention can be obtained, even if it is caused by industrially unavoidable processing accuracy, or even if there is a partially discontinuous part within a few μm, intentionally or unintentionally. Included in "continuous". The above-mentioned "periodic" and "trigonometric function" have the same meaning, and the same applies thereafter.

Here, the mode of change of the duty ratio in the axial direction of the grid can be classified into a case where the duty ratio changes according to a periodic function in a mathematical sense and a case where the duty ratio changes substantially periodically but with randomness. In the former case, it functions as a diffraction grating having a predetermined period, and problems such as generation of a diffracted rainbow may occur. Therefore, in order to reduce this effect, as in the latter case, as the mode of changing the duty ratio, a substantially periodic change is preferable, and it is more preferable that a random fluctuation exists.

The material of the birefringent layer 20 is not particularly limited as long as it can transmit light to be depolarized and can form the above-mentioned grid structure (pattern shape), and is appropriately selected according to the purpose. can do. For example, the surface layer portion of the translucent substrate 10 may be processed to form a grid structure, and the surface layer portion may be used as the birefringent layer 20. The grid structure may be formed by machining, or may be formed by etching such as wet etching and dry etching. As long as the required processing accuracy can be obtained, the grid structure may be formed by any method, but considering the required fine accuracy, it is preferable to form the grid structure by dry etching.

Further, when a layer of a material different from that of the translucent substrate 10 is formed on the translucent substrate 10 and the formed layer is etched to form a grid structure to form a birefringent layer 20, the refractive index is increased. It is preferable to use a large material, it is more preferable to use an inorganic material, and it is particularly preferable to use an inorganic oxide such _{as Nb 2} O ₅ , Ta ₂ O ₅ , TiO ₂ , SiO _{2, etc. as such an inorganic material.} .. This is because the larger the refractive index, the larger the birefringence caused by the same grid height H, so that the etching amount can be reduced and the accuracy of forming the grid structure can be easily improved. _{Among them, Nb 2} O ₅ , Ta ₂ O ₅ , and TiO ₂ , which are high refractive index materials, are preferable, and Nb ₂ O ₅ is the most preferable. When Nb ₂ O ₅ is used for the birefringent layer 20, the etching selectivity with the etching mask material layer described later becomes large, so that deeper grooves can be easily formed and retardation can be increased.

Hereinafter, birefringence and retardation according to a specific example when _{niobium oxide (Nb 2} O ₅ ) is used as the birefringence layer 20 in the depolarizing plate 100 according to the present embodiment will be described. In FIG. 2 (A), shows the change of the effective birefringence of the _{n TM} and _{n TE} for Duty ratio of the grid structure, showing the retardation variation of the relative Duty ratio of the grid structure in FIG. 2 (B). The refractive index of niobide oxide as a high refractive index material used for the birefringent layer is 2.3, and the refractive index of air in the low refractive index portion, which is a gap between grid structures, is calculated as 1. In this case, when the duty ratio is 0.6, the birefringence Δn and the retardation Re are maximized. The duty ratio at which birefringence and retardation are maximized varies depending on the refractive index of the material used for the birefringence layer 20. For example, when silicon oxide (SiO ₂ ) is used, the duty ratio becomes maximum within the range of 0.5 to 0.55. It is preferable to change the duty ratio within the range of 0.2 or more and 0.6 or less because the amount of change in retardation can be maximized when various materials are used for the birefringence layer 20.

For example, when depolarizing red light having a wavelength of about 660 nm, retardation of half a wavelength (that is, 330 nm) or more is required for depolarizing. When niobium oxide is used, when the range in which the duty ratio changes depending on the formed grid structure is 0.2 to 0.6, and the grid height H is 1470 nm or more, the polarization of the red light is surely eliminated. can do. The above calculation example is only one specific example. It goes without saying that each parameter is appropriately designed according to the material of the birefringent layer to be used, the wavelength of the light to be depolarized, and the grid structure to be formed. As the wavelength becomes longer, it is necessary to increase the grid height H in order to obtain the same retardation. Therefore, when depolarizing green or blue light having a shorter wavelength than red, the grid height H is the above. If it is 1470 nm, polarization can be reliably eliminated.

As shown in the above specific example, when the grid structure is formed by etching, the grid height H (groove depth) is relatively large compared to the gap width G (groove width) between adjacent grids. .. In other words, a pattern of a grid structure having a relatively large so-called "aspect ratio" is formed by etching. Here, the smaller the aspect ratio is, the easier it is to form the grid structure, which is preferable in manufacturing the depolarizing element. Therefore, it is preferable to use a material capable of reducing the aspect ratio for the birefringent layer in order to fabricate the depolarizing element.

As will be described later in the examples, if the pitch width of the grid structure is 140 nm and the duty ratio is 0.2 to 0.6, the gap width G is 56 nm (duty ratio is 0. It varies from 6) to 112 nm (duty ratio is 0.2). Therefore, if the grid height H (which can be said to be the etching depth) is 1470 nm, the aspect ratio of the grid structure is in the range of 13 to 26. It should be noted that this merely shows the aspect ratio of one specific example, and the range of the aspect ratio is not limited to any specific value in the present embodiment.

Here, the degree of change from the maximum value to the minimum value of the duty ratio in the grid axis direction is not particularly limited, and the polarization of the incident light can be eliminated. Therefore, the degree of change in the duty ratio is determined by the depolarizing element 100. It may be determined as appropriate according to the environment in which it is used. The change from the maximum value to the minimum value of the duty ratio in the grid axis direction may be referred to as a period in the grid axis direction, but as described above, the change in the duty ratio in the grid axis direction is not a periodic change. Is preferable, so it is referred to as "degree of change". Of course, there is an optimum form of the degree of change in the duty ratio depending on the environment in which the depolarizing element 100 according to the present embodiment is used. For example, when the depolarizing element 100 is applied to a simple incident light such as a Gaussian beam, the change from the maximum value to the minimum value of the duty ratio in the periodic change in the grid axis direction is within a range smaller than the luminous flux diameter. Is preferable. This is because if the luminous flux diameter is smaller than the degree of change in the duty ratio, the change width of the retardation in the luminous flux becomes small and the polarization elimination may be insufficient. For example, in the case of a laser beam having a beam diameter of 1 mmΦ, the range from the maximum value to the minimum value of the duty ratio in the periodic change in the grid axis direction is preferably 1 mm or less.

When the depolarizing element 100 is used in an environment such as a projector in which light from each pixel of an LCD or DLP is imaged on a screen via a projection lens, it is as simple as the Gaussian beam described above. The example of light flux diameter cannot be applied. For example, when the depolarizing element 100 according to the present embodiment is arranged near the projection lens, the diameter of the lens or the diameter of the aperture diaphragm corresponds to the diameter of the luminous flux (for example, several tens of mm). On the other hand, when the depolarizing element 100 is arranged near the pixels, the luminous flux diameter is about several times the size of each pixel (for example, several μm). Therefore, depending on the environment in which the depolarizing element 100 is applied, the range from the maximum value to the minimum value of the duty ratio in the periodic change in the grid axis direction may be set to about 10 μm.

Further, in the depolarizing element 200 according to the preferred embodiment according to the present invention, it is preferable that the birefringent layer 20 is covered with the protective film 50 as shown in FIGS. 3A and 3B. Regarding the grid width W and the gap width G, FIG. 3A corresponds to a schematic view in which the protective film 50 is provided in FIG. 1B, and FIG. 3B is protected in FIG. 1C. Corresponds to the schematic diagram provided with the film 50. In an optical element having a grid structure, the optical characteristics may change due to the adsorption of moisture or the like to a part of the optical element. To prevent this, a protective film is formed on the grid structure to deteriorate the optical characteristics due to the usage environment. This is because it is possible to suppress. For example, in terms of hardness and barrier properties, _{it is preferable to form a protective film 50 made of SiO 2,} and such a protective film 50 can be formed by a sputtering method or a CVD method. In order to prevent changes in optical characteristics due to the formation of the protective film 50, it is particularly preferable to form the protective film 50 while leaving voids between adjacent grids, as shown in FIGS. 3A and 3B. preferable. Further, in order to prevent reflection, an AR coat or the like made of a multilayer film of a dielectric may be further formed on the front and back surfaces of the depolarizing element 200.

(Optical equipment)
The optical instrument of the present invention is equipped with at least a depolarizing element according to the present invention, and further has other configurations, if necessary.

(Liquid crystal display device)
The liquid crystal display device of the present invention is equipped with at least a depolarizing element according to the present invention, and further has other configurations, if necessary.

(Manufacturing method of depolarizing element)
Next, an embodiment of a method for manufacturing a depolarizing element according to the present invention described above will be described with reference to FIG. It should be noted that the embodiment described below is only one embodiment of the method for manufacturing a depolarizing element according to the present invention, and the depolarizing element according to the present invention may be manufactured by another embodiment. Except for the step of forming the resist layer 40 by providing a pattern of a grid structure on the resist material layer 40'described later, in each step of the present embodiment, film formation, processing, etc. can be performed according to a conventional method.

In the present embodiment, first, as shown in FIG. 4A, the translucent substrate 10 is prepared. Next, the birefringent material layer 20'is formed on the surface of the translucent substrate 10 by sputtering or the like. The above-mentioned material used for the birefringent layer 20 can be applied to the birefringent material layer 20'. The film thickness of the birefringent material layer 20'is the grid height H of the depolarizing plates 100 and 200.

As shown in FIG. 4C, in order to control the aspect ratio after the formation of the birefringent material layer 20', the etching mask material layer 30' made of a material having an appropriate etching selectivity is used as the birefringent material. It is preferably formed on the surface of layer 20'. The aspect ratio can be reduced by using a material having a large etching selectivity. As the etching mask material layer 30', Al, Ti, Ta, Si, Cr and the like can be used, and it is preferable to use Al in order to increase the etching selectivity.

Next, as shown in FIG. 4D, it is preferable to form the resist material layer 40'on the etching mask material layer 30'. As the material of the resist material layer, for example, ArF resist, KrF resist, i-line resist and the like can be used, although it depends on the wavelength of the laser used in the interference exposure method performed in the subsequent step.

Here, it is preferable to form a pattern similar to the grid structure of the birefringence layer 20 described above by using the two-luminous flux interference exposure method. That is, as shown in FIG. 4 (E), first, the formed resist material layer is subjected to two-luminous flux interference exposure. In this interference exposure, the first interference exposure forming the main grid and the second interference exposure for providing a periodic change in the duty ratio in the plane are divided into two stages of two-luminous flux interference exposure. I do. Here, the optical system is adjusted so that the period of the interference fringes is set to the pitch width P for the first time and a period larger than the pitch width P for the second time. When development is performed with an alkaline developer or the like after exposure, a resist layer 40 having a resist pattern in which the duty ratio changes along the grid axis direction is obtained.

Then, using the obtained resist layer 40 as an etching mask, the mask material layer 30'is etched with, for example, chlorine gas, and the resist pattern is transferred to obtain the mask layer 30 (FIG. 4 (F)). Next, the obtained mask layer is used as an etching mask, and the pattern shape is transferred by etching the birefringent material layer 20'by dry etching using a fluoride gas or the like to obtain the birefringent layer 20 (FIG. 4 (G). )). Finally, if the residual mask layer 30 is removed, the depolarizing element 100 can be obtained (FIG. 4 (H)).

In the present embodiment, it is not necessary to use an optical crystal as a material and it is not necessary to use a costly process such as stepper exposure when manufacturing the depolarizing element 100. Therefore, the depolarization plate can be provided relatively easily as compared with the prior art. Further, the obtained depolarizing plate 100 can be composed of only an inorganic material, and is suitable for application even in a high temperature environment.

Further, it is also preferable that the protective film 50 covering the birefringent layer 20 is formed on the depolarizing element 100 thus obtained by the above-mentioned sputtering, CVD or the like to form the depolarizing element 200 (FIG. 4 (I)). ..

In this embodiment, the pitch width P is preferably less than 200 nm, the pitch width P is preferably constant, and the height H of the grid structure is preferably constant. By doing so, the depolarizing elements 100 and 200 can be manufactured by a relatively simple method at low cost.

(Example 1)
_{An Nb 2} O ₅ layer (which becomes a birefringent layer) was formed on the surface of the glass substrate by a sputtering method to a thickness of 1470 nm. Next, an Al layer was formed with a thickness of 200 nm as a layer to be an etching mask film. Further, an antireflection BARC (manufactured by Tokyo Ohka Co., Ltd .; SWK-EX4) having a film thickness of 40 nm was formed with a spin coater, and a photoresist for KrF (manufactured by Tokyo Ohka Co., Ltd .; TDUR-P3262) was further applied with a spin coater film thickness of 200 nm. Next, using a laser with a wavelength of 266 nm, the duty ratio changes in a range of 0.2 to 0.6, and is divided into two stages under the following conditions so that the duty ratio changes continuously along the grid axis direction. Two-luminous flux interference exposure was performed.
・ Double luminous flux interference exposure condition 1st time: interference fringe period 140 nm
Second time: Interference fringe period 1000 μm
After the exposure, it was developed with an alkaline developer to obtain a resist pattern similar to the shape shown in FIG. 1 (A). Next, the obtained resist pattern was used as an etching mask, and the Al layer was etched using chlorine gas. Further, using this Al pattern as a mask, the Nb ₂ O ₅ layer was etched by dry etching using a fluoride gas. In O ₂ ashing, the resist remainder was also removed. As described above, a grid structure having a grid height of 1470 nm made of _{Nb 2} O _{5 was formed on the glass substrate to obtain the depolarizing element according to the first embodiment.} The maximum value W _max of the grid width was 84 nm, and the minimum value W _min was 28 nm. The distance between the position where the adjacent grid structure duty ratio became the maximum and the position where the adjacent grid structure duty ratio became the minimum was about 500 μm, which was substantially constant.

The retardation according to the obtained grid structure is 950 nm at the maximum portion of the grid width and 540 nm at the minimum portion. When light having a beam diameter of about 3 mmφ is incident so as to include the maximum portion and the minimum portion of the retardation at the same time, the transmitted light receives the retardation of 330 nm (727 nm-397 nm) at the maximum, although the transmitted light varies depending on the position. Therefore, when linearly polarized light having a wavelength of 660 nm forming an angle of 45 degrees with the grid axis direction is incident, the passed light contains light components in various polarized states from linearly polarized light to elliptically polarized light to circularly polarized light. As described above, the depolarizing element according to the first embodiment has a function of depolarizing the incident light.

(Examples 2 to 6)
Table 1 shows only the material and pitch width P of the birefringent layer so that the difference in the obtained polarization is 330 nm at the maximum and the duty ratio changes continuously within the range of 0.2 to 0.6. The depolarizing element according to Examples 2 to 6 was produced in the same manner as in Example 1 except that the conditions were changed as shown. As the material of the layer to be the birefringence layer is _{changed from Nb 2} O ₅ to SiO ₂ and the pitch width P is changed from 140 nm to 100 nm or 200 nm, the grid height H, the grid width W _max and the gap width G _min Was also shown in Table 1. The maximum value of the aspect ratio is also shown in Table 1.

In Example 2, the maximum value of the aspect ratio was 177, which was larger than that in Example 1, but it was confirmed that the polarization could be eliminated. In Example 3, it was confirmed that the polarization could be reliably eliminated as in Example 1. In Example 4, the maximum value of the aspect ratio was 248, which was larger than that in Example 2, and the etching accuracy became strict, but it was confirmed that the polarization could be eliminated as in Example 1. In Examples 5 and 6, the pitch width is large and the transmittance may be dip, and there is a concern that the yield may be deteriorated in the case of mass production, but the polarization itself can be eliminated.

According to the present invention, it is possible to provide a depolarizing element that can be manufactured relatively easily as compared with a conventional depolarizing element and that can reliably depolarize.

10 ... Translucent substrate 20 ... Birefringence layer 20'... Birefringence material layer 30 ... Mask layer 30'... Mask material layer 40 ... Resist layer 40'... Resist material Layer 50: Protective film 100, 200: Depolarizing element P: Pitch width W: Grid width G: Gap width H: Grid height

Claims (12)

Translucent board and
It has a birefringent layer provided on the translucent substrate, arranged at a pitch width equal to or less than the wavelength of incident light, and having a one-dimensional grid structure.
A depolarizing element (provided that a silicon dioxide convex pattern, a silicon dioxide concave pattern, and adjacent silicon dioxide) are characterized in that the duty ratio of the grid structure changes continuously along the axial direction of the grid structure. Except for optical elements in which all three patterns of silicon dioxide strut patterns that connect the ridge patterns to each other are formed.) The depolarizing element according to claim 1, wherein the duty ratio changes within a range of 0.2 or more and 0.6 or less. The depolarizing element according to claim 1 or 2, wherein the pitch width is less than 200 nm. The depolarizing element according to any one of claims 1 to 3, wherein the height of the grid structure is constant. The depolarizing element according to any one of claims 1 to 4, wherein the retardation of the birefringent layer changes continuously in the plane of the translucent substrate. The depolarizing element according to any one of claims 1 to 5, wherein the birefringent layer is made of only an inorganic material. The depolarizing element according to any one of claims 1 to 6, wherein the birefringent layer is covered with a protective film. The depolarizing element according to any one of claims 1 to 7, wherein the pitch width is constant. The depolarizing element according to any one of claims 1 to 8, wherein the duty ratio of the grid structure changes substantially periodically with respect to the axial direction. The method for manufacturing the depolarizing element according to any one of claims 1 to 9.
A method for manufacturing a depolarizing element, characterized in that the grid structure is formed by using a two-luminous flux interference exposure method. An optical device comprising the depolarizing element according to any one of claims 1 to 9. A liquid crystal display device comprising the depolarizing element according to any one of claims 1 to 9.

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