JP2007316270A - Manufacturing method of optical component, retardation element and polarizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a minute grating having small shape variation and to reduce fluctuation of phase difference even when an optical component such as a retardation plate has a large aspect ratio of the grating. <P>SOLUTION: A dielectric 12 (for example, a SiO<SB>2</SB>film) is formed on a glass substrate 11, tungsten silicide is film-formed thereon as a metal mask layer 13 for pattern matching (Fig.1(b)) and then a photoresist layer 14 is formed. Then a metal mold, on the surface of which the minute grating is formed, is pressed to the photoresist layer 14 to transfer a metal mold pattern to the resist and then the metal mold is released to form a minute grating pattern as shown in Fig.1(d). Thereafter the mask layer 13 is subjected to patterning (etching) by using the patterned photoresist 14 as the mask and then the photoresist layer 14 is removed. Further the dielectric 12 on the glass substrate 11 is subjected to patterning by etching by using the patterned mask layer 13 and then the mask layer 13 is removed (Fig.1(h)). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an optical component, a retardation element, and a polarizer, and relates to the production of a fine grating shape used for an artificial optical anisotropic medium such as a polarizing plate and a retardation plate.

  The retardation plate (retarder) that gives a desired phase difference between mutually orthogonal polarization components includes (1) an anisotropic optical crystal and (2) a polymer material arranged in one direction. Widely used. In the former, an optical crystal having birefringence is polished to a desired retardation, and in the latter, for example, a sheet-like material is stretched in a heat-softened state to be aligned in one direction, and stretching conditions There is a method of making the phase difference as desired.

  There is also a method using structural birefringence by a fine grating smaller than the wavelength of light. This uses the expression of birefringence when the pitch of the fine grating is smaller than the wavelength. If the refractive index ns in the direction parallel to the fine grating and the refractive index np in the vertical direction are used, the refractive index Respectively

  Given in. Here, p is the width ratio of the first medium to be set to the grating period, na is the refractive index of the first medium constituting the grating, and nb is the refractive index of the second medium. When used as a phase difference plate, the total phase difference becomes a problem. This is because the grating depth is d and the wavelength is λ.

  Given in.

In the case of using a fine grating, the magnitude of birefringence is determined by the refractive index difference between dielectrics constituting the grating, and the total phase difference is also determined by the grating depth. For example, if the first medium is SiO ₂ (na = 1.46) and the second medium is air (nb = 1.00), the grating depth is required to give a quarter wavelength phase difference to light with a wavelength of 600 nm. D = 150 / (1.46-1) = 326 nm.

When the first medium is Nb ₂ O ₅ (na = 2.28), the wavelength is 117 nm. Increasing the refractive index of the first medium requires less groove depth, but increases the reflection between the first medium and the input / output medium. Since the surface of a fine grating is uneven, it is difficult to form an antireflection film and it is difficult to suppress reflection. Therefore, the uppermost layer of the grating is preferably made of a material having a relatively low refractive index. However, since the birefringence obtained at a low refractive index is not large, the etching depth becomes deep and a groove shape with a high aspect ratio is required.

  For example, as shown in FIGS. 1 and 2, the fine pattern of the first medium is obtained by first pressing a mold (for example, 20 in FIG. 2) having a prepared uneven pattern with a pitch of 100 nm to the photoresist. The mold pattern is transferred to a resist, and then the first medium is etched using the photoresist on which the fine lattice pattern is formed as an etching mask.

  Therefore, the photoresist is required to have etching resistance, but in order to form a deep groove, it is necessary to increase the selectivity (ratio of etching rate) between the material to be etched (first medium) and the mask material.

FIGS. 1 and 2 show a manufacturing process of a fine lattice. First, in FIG. 1A, a dielectric 12 (for example, SiO ₂ film) is formed on a glass substrate 11, and a pattern matching mask layer is formed thereon. 13 is formed (FIG. 1B), and then a photoresist layer 14 is formed by coating (FIG. 1C).

  Next, as shown in FIGS. 2A to 2C, when the mold 20 having the fine lattice formed thereon is pressed against the photoresist layer 14 to transfer the mold pattern to the resist, the mold is released. A fine lattice pattern is formed as shown in FIG.

  Thereafter, the mask layer 13 is patterned (etched) using the patterned photoresist (14) as a mask (FIG. 1E), and then the photoresist layer 14 is removed (FIG. 1F).

  Next, as shown in FIG. 1G, the dielectric layer 12 on the glass substrate 11 is patterned by etching using the patterned mask layer 13, and then the mask layer 13 is removed (FIG. 1H).

In the above description, for example, when the dielectric is SiO ₂ , a CF compound gas such as CF ₄ is used. In this case, the selectivity with respect to the resist is 2 to 3. In this case, a resist having a thickness of 200 nm is required to etch a groove having a depth of 400 nm. The resist thickness after the mold pattern is pressed is determined not by the coating film thickness but by the depth of the convex and concave portions of the mold itself. As a result, a mold 20 having a groove depth of 200 nm is required, but it is difficult to release the mold and the photoresist during transfer. In particular, when a technique such as lift-off is used, the resist cross-sectional shape must be inversely tapered, and this mold release becomes more difficult.

  As a method for avoiding this problem, another mask material (for example, a metal material) having a higher etching resistance than that of the resist (having a high selection ratio) is formed between the dielectric and the resist. Etching is then performed, and then the dielectric is etched using the metal material as a mask.

For example, if Al is used as the mask material, the selectivity ratio between SiO ₂ and Al is> 10, the selectivity ratio between resist and Al is ˜3, and even when a 400 nm groove is formed in the dielectric, the mold groove is A depth of <100 nm is sufficient.

Conventionally, as an optical wavelength plate provided with a concavo-convex lattice pattern, for example, the one described in Patent Document 1 below has been proposed.
JP 2005-242083 A

  However, as described above, when Al, Cr or the like is used as an etching mask, it is often polycrystallized. The etching rate is different between the crystal and the boundary portion, and since the grain size is approximately the same as the wavelength, the straight line becomes uneven after etching.

  When the dielectric is etched using such a mask whose boundary is uneven, the fine lattice of the dielectric itself is transferred as it is as shown in FIG. For this reason, even if the groove depth is uniform, the magnitude of birefringence obtained when the grating shape is uneven fluctuates, thereby causing a problem that a desired phase difference cannot be obtained.

  The present invention relates to the production of a fine grating shape used for an artificial optical anisotropic medium such as a polarizing plate and a retardation plate, and to obtain a fine grating with little shape variation even if the aspect ratio of the grating is large. Objective.

  In order to avoid etching shape deterioration due to crystal grain boundaries in a polycrystalline film, it is effective to use an amorphous film. For example, when a tungsten silicide alloy is used as an etching mask, a film in an amorphous state can be easily obtained, and by using this as an etching mask, unevenness of the etching boundary surface due to the grain boundary is suppressed, and a desired position can be obtained. A phase difference can be obtained stably.

  Therefore, the method for manufacturing an optical component of the present invention for solving the above problems includes a step of forming a dielectric on a substrate, and a step of forming a fine lattice by etching the dielectric using a tungsten silicide alloy as an etching mask. It is characterized by having.

  The retardation element of the present invention is manufactured by forming a dielectric on a substrate and etching the dielectric using a tungsten silicide alloy as an etching mask to form a fine grating.

  The polarizer of the present invention is manufactured by forming a metal or semiconductor on a substrate and etching the metal or semiconductor using a tungsten silicide alloy as an etching mask to form a fine lattice.

  In the above structure, by using a tungsten silicide alloy as an etching mask, even a relatively large aspect ratio lattice can be manufactured. Further, since a film in an amorphous state can be easily obtained, unevenness of the etching boundary surface due to the polycrystalline grain boundary is suppressed, and a fine lattice with little shape variation can be obtained.

(1) According to the first to third aspects of the present invention, in the anisotropic optical device using the structural birefringence by the fine grating, the occurrence of the irregular shape on the grating side surface is suppressed, and as a result, the phase difference fluctuates. Can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

  As an embodiment of the present invention, a manufacturing process of an optical component, for example, a retardation plate such as a quarter-wave plate will be described with reference to FIGS. As shown in FIG. 2A, a mold 20 made of SOI (silicon on insulator) having a fine grating of 100 nm depth and 100 nm pitch formed on the surface by two-beam interference exposure in advance is prepared. A demolding agent may be formed on the surface of the mold 20 so as to improve the releasability during transfer.

First, a 400 nm thick SiO ₂ film (dielectric 12) is formed on a borosilicate glass substrate 11 by sputtering (FIG. 1A). Further, as shown in FIG. 1B, WSi (tungsten silicide) is formed as a metal mask layer for patterning to a thickness of 40 nm by sputtering (mask layer 13), and then a photoresist is formed to a thickness of 300 nm. A photoresist film (14) is formed by coating (FIG. 1 (c)).

  Next, as shown in FIGS. 2A to 2C, the prepared mold 20 is pressed against the resist film (14), and in this state, the resist is cured by irradiating UV (ultraviolet rays) from the back surface of the substrate 11. After that, the mold 20 is released from the resist surface. FIG. 1D shows a state where the mold has been released. When the shape of the resist was measured, almost the same shape as that of the mold 20 was obtained.

Next, as shown in FIG. 1E, in a RIE (reactive ion etching) apparatus, CF ₄ and SF ₆ are used as etching gases, and a patterned photoresist film (14) is used to form a metal mask layer (13 ).

  RIE (Reactive Ion Etching) always has both physical and chemical etching reactions, and can be optimized by changing the balance between the two depending on the production conditions. Then, after patterning the metal mask layer (13), the photoresist film (14) is removed by oxygen plasma ashing (FIG. 1 (f)).

Next, as shown in FIG. 1G, the SiO ₂ layer is patterned by etching using a mixed gas of CHF ₃ and CH ₄ by RIE using the patterned metal mask layer (13), and then SF ₆ The metal mask layer 13 is removed using a gas (FIG. 1 (h)).

  When the cross section of the sample thus prepared was observed, it was confirmed that a fine lattice having a pitch of 90 to 110 nm and a groove depth of 380 nm was formed as shown in FIG. That is, as shown in FIG. 3B, the uneven shape on the side surface of the dielectric grating, which was observed when Al was used as the mask material, was not observed. Further, when the optical characteristics were also measured, the conventional birefringence fluctuation caused by the side surface irregularities of the grating was reduced, and the effect of the present invention could be confirmed.

  That is, when two quarter-wave plates using the fine grating according to the present invention (FIG. 3A) are arranged so that the optical axes are orthogonal to each other and linearly polarized light is incident, the degree of linear polarization is degraded. There wasn't.

  On the other hand, in the case of using the conventional fine grating (FIG. 3B), the degree of linear polarization was significantly deteriorated. This is due to the fact that the birefringence and the phase difference are locally changed by the fluctuation of the fine lattice shape.

  The retardation element of the present invention includes a fine grating produced by the method for producing an optical component.

  In addition, the polarizer of the present invention includes a fine grating manufactured by the method for manufacturing an optical component. In this case, a metal or a semiconductor is formed on the substrate instead of a dielectric, and tungsten silicide is formed. The metal or semiconductor is etched using an alloy as an etching mask to form a fine lattice.

Explanatory drawing which shows the whole manufacturing process of the fine lattice of one embodiment of this invention. Explanatory drawing which shows a part of manufacturing process of the fine lattice of one Embodiment of this invention. The difference of the grating | lattice shape by an etching mask is represented, (a) is a perspective view which shows the fine grating by this invention, (b) is a perspective view which shows the fine grating by a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Board | substrate, 12 ... Dielectric, 13 ... Mask layer, 14 ... Photoresist layer, 20 ... Mold.

Claims (3)

Forming a dielectric on the substrate;
And a step of etching the dielectric using a tungsten silicide alloy as an etching mask to form a fine lattice.   A retardation element manufactured by forming a dielectric on a substrate and etching the dielectric using a tungsten silicide alloy as an etching mask to form a fine grating. A polarizer manufactured by forming a metal or semiconductor on a substrate and etching the metal or semiconductor using a tungsten silicide alloy as an etching mask to form a fine lattice.

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