JP4999401B2 - Manufacturing method of optical element having fine irregularities on surface - Google Patents

Description

  The present invention relates to a method of manufacturing an optical element such as a phase plate having a fine uneven shape on the surface. The phase plate generates a phase difference between two orthogonal linearly polarized lights, and is used as a quarter-wave plate, a half-wave plate, a full-wave plate, and the like. Are used for writing / reading devices and other optical devices.

  In addition to a crystal-polished wave plate, the thickness of a birefringent material such as quartz is adjusted so that the phase difference between ordinary and extraordinary rays has a predetermined relationship to the wavelength. A grating-type wave plate utilizing the fact that the fine irregular surface formed by (2) exhibits birefringence is also used. The present invention relates to an optical element having a fine concavo-convex shape on its surface, such as the latter grating-type wave plate.

  A phase plate known as one type of optical element has an optical function of providing a phase difference between mutually orthogonal polarization components, and is used in various optical devices. Conventionally, phase plates using “uniaxial anisotropic crystals exhibiting birefringence” such as artificial or natural rutile, calcite, and quartz are known. "Natural crystals are difficult to obtain and expensive in" optically uniform and large shape ". Such a “phase plate using a crystal material” has a narrow operating wavelength range.

  Recently, a phase plate having a sub-wavelength structure (SWS) has been proposed as a “phase plate capable of functioning over a wide wavelength range” (Patent Documents 1 and 2). The optical action of the subwavelength structure is described in Non-Patent Document 1 and the like. Moreover, the thing of a nonpatent literature 2 is known as an example of the formation method of a subwavelength structure.

Patent Document 1 discloses a phase plate in which a sub-wavelength structure is formed as a “surface structure of a glass substrate”. Patent Document 2 discloses a “phase plate in which a lattice structure is transferred in a plane using a parallel plate as a substrate”, but does not describe any material of a portion to which the parallel plate or the lattice structure is transferred.
Non-Patent Document 2 discloses a thermal nanoimprint method using a resin bulk material as a method for forming a subwavelength structure.

As another production method, there is a method of forming a groove structure using a dry etching method. As this method,
(1) A structure in which a substrate material is grooved by dry etching;
(2) A method has been proposed in which a high refractive index material is formed on a substrate material and dry-etched.
JP-A-2005-44429 JP 2005-106901 A Hisao Kikuta, "Structural Birefringence and Its Application to Optical Elements" (Introduction to first-order diffractive optical elements on May 20, 1997) p158-167 Published by Optronics KONICA MINOLTA TECHNOLOGY REPORT VOL.2, (2005) p97-100 “Fabrication of subwavelength structured broadband waveplate using nanoimprint technology”

  A sub-wavelength grating made of a resin material by the nanoimprint method is inferior in environmental resistance (light resistance, temperature and humidity resistance), reliability, and long-term stability because it is made of a resin material. In addition, since the resin material is shaped and manufactured, the flow viscosity of the resin material cannot be lowered. Therefore, the resin flow during molding is poor, and it is not easy to realize a high aspect structure. To realize a high aspect structure, a high aspect structure mold is required, but it is not easy to manufacture a high aspect structure mold. Eventually, the sub-wavelength grating becomes expensive even by the nanoimprint method.

  The dry etching method has a problem of pattern perpendicularity during dry etching. This is because, during dry etching, the etching species that act on the substrate (chemical reaction species that actually contribute to etching) become harder to reach the etching point as the pattern depth becomes deeper. It becomes difficult for the etching species to be discharged from the recess formed by etching. For this reason, variations in processing depth, variations in bottom shape, and the like occur. As a result, the variation in the processed substrate and the variation between batches become large, and it is difficult to stabilize the quality.

It is difficult to produce a sub-wavelength structure with a high aspect ratio by either method.
Furthermore, there is another problem that the filling factor (FF = L / P ratio) of the concavo-convex structure defined later with reference to FIG. 4 cannot be increased. P is the pitch of the uneven structure, and L is the land width.

  The present invention provides a manufacturing method that can inexpensively manufacture an optical element excellent in environmental resistance (light resistance, temperature and humidity resistance), reliability, and long-term stability, and can increase a filling factor. It is for the purpose.

One embodiment of the present invention is an optical element for manufacturing an optical element having a fine concavo-convex structure having a rectangular cross-sectional shape made of a dielectric on at least one surface of a substrate, including the following steps (A) to (C). It is a manufacturing method.
(A) a step of forming a pattern having irregularities opposite to the fine concavo-convex structure by the resin ridges arranged on the substrate surface;
(B) A film forming step of filling the concave portions of the pattern with a dielectric layer by a film forming method, and (C) a step of removing the resin.

  A preferable example of the step (A) is a shape transfer step by an imprint method in which a resin layer is formed by applying a resin to the substrate surface, and after pre-baking, the mold having the fine uneven structure is pressed against the resin layer. .

In another embodiment of the present invention, an optical element in which a fine concavo-convex structure having a rectangular cross section made of a dielectric is formed on at least one surface of a substrate and silsesquioxane is present in a gap between the fine concavo-convex structures is described below. A process for producing an optical element comprising the steps (A) and (B).
(A) Silsesquioxane is applied to the substrate surface to form a silsesquioxane layer, and after pre-baking, the silsesquioxane layer is pressed against the mold having the fine concavo-convex structure by an imprint method. After performing shape transfer, the step of thermally curing the silsesquioxane to form a pattern having concavities and convexities opposite to the fine concavo-convex structure by means of the ridges of silsesquioxane, and (B) the pattern by a film forming method Film forming step of filling the recesses with a dielectric layer.
Since silsesquioxane has a quartz structure when cured, it has excellent durability and environmental resistance even if it remains in the optical element. The refractive index of the cured silsesquioxane is about 1.45.

The fine concavo-convex structure in the optical element of the present invention is not a resin material but a dielectric material filled in the concave portions in the step (B). As such a dielectric material, TiO ₂ , Ti ₂ O ₅ , Nb ₂ O ₅ , In ₂ O ₅ , SnO ₂ , Al ₂ O ₃ , CrO ₂ , ZrO ₂ , and antireflection film material are used. MgF ₂ , Highcom (Merck's trade name: ZrO ₂ + TiO ₂ ), OM-10 (Merck's trade name: Ta ₂ O ₅ + TiOn, where n is the number of oxygens, and this compound is in a Ti deficient state. OM-4 (trade name of Merck), H-4 (trade name of Merck), M-4 (trade name of Merck), and the like can be used.

  Since the optical element is composed of a dielectric material, both the optical element in the form of removing the resin and the optical element in the form of remaining using silsesquioxane as the resin are resistant to the environment (light resistance, resistance to light). Temperature and humidity), reliability and long-term stability.

  In step (B), the recess is filled with a dielectric material. In the method of forming irregularities by the dry etching method, in order to increase the filling factor, a narrow space must be formed by etching. In the method of the present invention, a dielectric material is formed by film formation in a wider space. Since the filling factor can be increased by filling the material, it is easy to manufacture a product having a large filling factor (the larger the value, the wider the band and the higher the stability).

  The step (B) preferably includes a bias plasma film forming step performed by applying a bias voltage to the substrate side in the middle thereof. In the bias plasma film forming process, the dielectric material, which is the film forming material, is incident on the substrate in the vertical direction, so that the film is satisfactorily formed on the bottom of the concave portion of the pattern, and the concave portion is filled with the dielectric layer. It becomes easy.

  The bias plasma deposition step preferably includes a substrate bias etching step in which reverse sputtering is performed with a bias voltage applied to the substrate side. In the substrate bias etching process, the reverse sputtering particles are concentrated and incident on the convex portion of the surface, so that the dielectric layer formed on the upper surface of the convex surface of the resin pattern is selectively and intensively removed by sputtering.

Here, a film forming process for filling a concave portion of a fine concavo-convex pattern in a line / space consisting of repetition of a ridge pattern (line) and a concave ridge pattern (space) with a dielectric layer will be considered.
When this film formation is performed by a conventional method in which a bias voltage is not applied to the substrate side, the film formation material deposited on the top of the line pattern grows also on the space side, so that the film formation material reaches inside the space. The deposited film thickness in the space is limited. Further, since the film forming material is less likely to reach the space than the line pattern, the deposited film thickness in the space becomes non-uniform. As a result, the conventional film forming method cannot be used in the present invention.

  In the bias plasma film forming process, the film forming material is incident on the substrate in the vertical direction, so that the film forming material easily reaches the bottom of the space. In this case, the film forming material deposited on the top of the line pattern is Since it is unavoidable to grow on the space side, the deposited film thickness in the space is limited.

  In the case of including a substrate bias etching process in which reverse sputtering is performed with a bias voltage applied to the substrate side, the film deposition material deposited on the top of the line pattern is removed by the reverse sputtering particles in the substrate bias etching process. The film forming material deposited on the top of the line pattern is prevented from growing on the space side, and the film forming material is uniformly deposited in the space.

  The dielectric layer filled in the recesses in the step (B) may be a single layer or a multilayer film structure. In the case of a multilayer film structure, the refractive index structure is preferably a thin film structure whose surface has an antireflection effect. Thereby, the antireflection effect can be given to the surface of the ridge of the concavo-convex structure of the obtained optical element.

As an example of the process (A), a mold used when applying a process by imprint method in which a resin layer is applied to the substrate surface and a mold having a fine concavo-convex structure is pressed against the resin layer is as follows. It is preferable to manufacture.
(A) forming a mask pattern having a planar pattern of a fine relief structure to be obtained by using a mask material on the (110) surface of a silicon substrate;
(B) a step of etching the silicon substrate with an alkaline solution using the mask pattern as a mask to form fine irregularities having {111} planes on side surfaces; and (c) a step of removing the mask pattern thereafter.

  When the (110) plane of the silicon substrate is etched with an alkali solution, anisotropic wet etching is performed in which etching proceeds in a direction perpendicular to the substrate surface so that the inner surface of the resulting recess becomes a {111} plane. Since this method can form irregularities with a high aspect ratio, a mold with a high aspect ratio can be manufactured.

According to the manufacturing method of the present invention, a highly durable optical element excellent in environmental resistance, reliability, and long-term stability can be realized. Since this method has high reproducibility of the manufacturing process, there is little product variation. Further, since the yield can be improved, the optical element can be manufactured at a low cost.
Since the filling factor can be increased, it is easy to realize a broadband wave plate.

First, an example of an optical element to be manufactured by the method of the present invention will be described.
FIG. 1 is a diagram for explaining an embodiment of a phase plate.
As shown in FIG. 1A, the phase plate has a configuration in which thin layers 12a and 12b are formed on both surfaces of a parallel flat glass plate 11. The thin layers 12a and 12b are preferably made of a material having a refractive index of 1.6 or more, and a fine concavo-convex structure having a rectangular wave shape in cross section is formed as a sub-wavelength structure.

  Terms will be described with reference to FIG. FIG. 1B schematically shows a fine concavo-convex structure having a rectangular cross section formed in a thin layer. The unevenness of the fine unevenness structure has a rectangular wave shape as shown in the cross-sectional shape, and such a rectangular wave-like unevenness extends in a direction perpendicular to the paper surface. Accordingly, the convex portions in the fine concavo-convex structure form long ridges extending in the direction perpendicular to the paper surface, and the concave portions also form long ridges extending in the direction perpendicular to the paper surface. The convex portion forming the ridge is called “land”, and the concave portion forming the ridge is called “space”.

  As shown in the drawing, the pitch P of the fine concavo-convex structure having a rectangular wave shape in cross section is the sum (L + S) of a land width L and a space width S of a pair of lands and spaces. The height of the land with respect to the space bottom is defined as a groove depth H.

  At this time, the filling factor (FF) is L / P and the aspect ratio is H / S. That is, a large filling factor means that the land width L occupying the pitch P is large (the space width S is small), and the groove depth H with respect to the land width L is larger as the aspect ratio is larger. The larger the aspect ratio, the more difficult it is to form a fine relief structure.

  As known from Non-Patent Documents 1 and 2 and the like, if the fine concavo-convex structure is a sub-wavelength structure, light having a wavelength larger than the pitch is not diffracted and is transmitted as it is as zero-order light (transmission at this time The rate is referred to as “0th-order transmittance”.

  That is, as shown in FIG. 1C, in the incident light incident on the fine concavo-convex structure from the air region, the polarization component TM oscillating parallel to the periodic direction (left-right direction in the figure) of the fine concavo-convex structure, the land longitudinal direction ( The fine concavo-convex structure acts like a medium having a different refractive index with respect to the polarization component TE that vibrates in parallel with the direction perpendicular to the paper surface.

If the effective refractive index in the portion of the fine concavo-convex structure is n (TM) for the polarization component TM and n (TE) for the polarization component TE, these effective refractive indexes are the refraction of the thin layer material on which the fine concavo-convex structure is formed. It is expressed as follows using the rate n and the filling factor f of the fine relief structure.
n (TE) = {fn ² + (1−f)} ^1/2 (1)
^{n (TM) = [n 2} / {f + (1-f) n 2}] 1/2 (2)

  For this reason, the phase of the polarization component TE is delayed by “δ” with respect to the polarization component TM in the transmitted light. That is, when the groove depth H is used, the optical thickness of the fine concavo-convex structure is “H · n (TM)” for the polarization component TM and “H · n (TE)” for the polarization component TE. Therefore, a phase delay δ is generated according to these optical thickness differences H {n (TE) −n (TM)}. This phase delay δ is retardation.

  If the optical thickness difference H {n (TE) -n (TM)} is D and the wavelength is λ, then δ = 2πD / λ. However, in the fine concavo-convex structure, over a wide region of the wavelength λ, A substantially constant retardation is obtained.

  n (TE) and n (TM) are determined by the refractive index n and the filling factor f of the thin layer material on which the fine concavo-convex structure is formed, and the retardation δ is the refractive index n, the filling factor f, and the groove depth H. Therefore, the retardation is eventually determined by adjusting the thin layer material (n is determined) on which the fine uneven structure is formed and the form of the fine uneven structure (the filling factor f and the groove depth H are determined). You can get things.

  When the fine concavo-convex structure is formed on both surfaces of the glass flat plate 11 as in the optical element shown in FIG. 1A, the retardation by the fine concavo-convex structure 12a is “δ1”, and the retardation by the fine concavo-convex structure 12b is “δ2”. Then, the retardation as the phase plate becomes “δ1 + δ2”.

  Therefore, in the case of the phase plate shown in FIG. 1A, the phase difference with respect to the polarization components TM and TE can be set to, for example, “π or π / 2” by adjusting the retardation (δ1 + δ2), and various wavelengths A board can be realized.

Next, a manufacturing method according to an embodiment for manufacturing the phase plate as described above will be described with reference to FIGS.
FIG. 2 shows a process of manufacturing a mold used in the process of applying the nanoimprint method.
(A) A silicon substrate 20 having a (110) surface is prepared as a mold substrate.
An electron beam drawing resist 22 is applied to the surface of the silicon substrate 20 and prebaked.
A pattern for forming a mold pattern is drawn on the resist 22 by an electron beam according to a preset program. This pattern is a pattern having a planar pattern of the fine uneven structure of the phase plate. The drawing conditions for electron beam drawing differ depending on the pitch and line width of the target phase plate.

  (B) The resist 22 drawn with the electron beam is developed and rinsed to form a resist pattern 22a. Thereafter, the resist pattern 22a is post-baked. This pattern 22a is a pattern in which the resist remains on the portion of the phase plate to be obtained that is to be a convex portion of the fine concavo-convex structure.

(C) The silicon substrate 20 is subjected to alkaline wet etching using the resist pattern 22a as a mask. Here, a KOH solution is used as an etching solution. However, hydrazine, EPW (a mixed solution of ethylenediamine / pithecatechol / water), TMAH (tetramethylammonium hydroxide), or the like may be used as the etching solution.
Since the surface of the silicon substrate 20 is the (110) plane, the etching of the silicon substrate with the alkali solution proceeds in a direction perpendicular to the substrate surface so that the {111} plane becomes the wall surface, and the pitch of the resist pattern 22a is increased. Etching in the depth direction while maintaining.

(D) The mold 24 is completed when the resist pattern 22a is removed. The removal of the resist pattern 22a is performed, for example, by performing an O ₂ ashing process on the silicon substrate 20. The mold 24 has a fine relief structure, and the pitch P, line width L, space width S, and filling factor (FF) L / P are the same as those of the target phase plate. The depth D of the fine concavo-convex structure is substantially equal to the target groove depth H of the phase plate.

Example 1
Next, the steps of the first embodiment in which a target phase plate is manufactured by forming a fine concavo-convex structure with a dielectric material on the product substrate 26 using the mold 24 will be described with reference to FIG.

3A and 3B show a process of forming a resin pattern on the product substrate 26. FIG.
(A) A parallel-plate light-transmitting quartz glass substrate having a flat surface is used as the product substrate 26. The product substrate 26 may be made of a glass material such as Pyrex (registered trademark) or Tempax (registered trademark).

  A transfer resin 28 is dropped on the surface of the substrate 26. As the transfer resin 28, UV (ultraviolet) curable resin or thermosetting resin can be used. When a UV curable resin is used, at least one of the product substrate 26 and the mold 24 needs to have a property of transmitting ultraviolet rays in order to cure the resin by ultraviolet irradiation. In this embodiment, since the mold 24 is a silicon substrate, the product substrate 26 needs to transmit ultraviolet rays. However, when a thermosetting resin is used as the transfer resin, neither the product substrate nor the mold needs to transmit light.

  The resin 28 preferably has a sufficiently low viscosity. As the UV curable resin, for example, PAK-01 (trade name of Toyo Gosei Co., Ltd .: viscosity 5-20 cp) or GRANDIC RC-8790 (trade name of Dainippon Ink Co., Ltd .: viscosity 2-10 cp) should be used. Can do. As the thermosetting resin, a PMMA (polymethyl methacrylate) resin material, a PMMA main component resist material, or the like can be used.

  The fine concavo-convex pattern surface of the mold 24 is pressed from above the resin 28 so as to be on the substrate 26 side. The concave / convex pattern of the mold 24 is transferred to the resin 28, and the resin enters the concave portion of the mold to form a pattern in which the resin protrusions extend in the direction perpendicular to the paper surface on the surface of the substrate 26.

  The resin 28 is cured. When the resin 28 is a photocurable resin such as a UV curable resin, light is irradiated from the substrate 26 side. In this embodiment, a silicon substrate is used as the mold 24. However, if a light-transmitting quartz glass substrate or the like is used as the mold, light can be irradiated from the mold side. When the resin 28 uses a thermosetting resin, it is heated and cured.

  (B) When the mold 24 is peeled after the resin 28 is cured, the resin pattern 28 a is formed on the substrate 26. The resin pattern 28a is a pattern in which ridges extending in the direction perpendicular to the paper surface are arranged in parallel to each other. The concavo-convex pattern formed by the surface of the substrate 26 and the resin pattern 28a is reverse to the concavo-convex pattern of the target phase plate.

A process of forming a fine concavo-convex structure for an optical element using a dielectric using the resin pattern 28a according to FIGS. 3C to 3I will be described.
(C) The substrate 26 is placed in a film forming apparatus that can apply a bias voltage to the substrate. Film formation is performed while rotating the substrate 26 in the in-plane direction. As the dielectric material to be formed, the above-mentioned various materials such as Ta ₂ O ₅ , TiO ₂ , Ti ₂ O ₅ , Nb ₂ O ₅ , In ₂ O ₅ , SnO ₂ , Al ₂ O ₃ , CrO ₂ are used. Can be used.

  In this film forming process, since a bias voltage is applied to the substrate, the dielectric material 30 as the film forming material is incident on the substrate 26 in the vertical direction, and the film is satisfactorily formed on the bottom of the concave portion of the resin pattern 28a. The

  (D) When the dielectric material 30 is deposited to an appropriate thickness, reverse sputtering is performed with the bias voltage applied to the substrate. At this time, since reverse sputtering particles, for example, argon ion particles, are concentrated and incident on the convex portion of the surface, the dielectric material 30 formed on the pattern is mainly sputtered and removed. The dielectric material 30 deposited on the bottom of the recess remains without being removed because the sputtered particles do not reach the recess.

  (E) Dielectric material 30 is formed again under the same conditions as in step (C). Here, the same material as the dielectric material 30 formed in the step (C) is formed, but a dielectric material having a different refractive index may be formed.

  (F) Reverse sputtering is performed as in step (D) to remove the dielectric material on the convex portions.

(G) Further, the dielectric material 30 is formed under the same conditions as in the step (C). In this case, a different dielectric material may be formed.
The film formation is performed until the height is almost the same as the resin pattern 28a. Preferably, the film formation process is completed when the dielectric material 30 is filled to a position slightly lower than the resin pattern 28a.

  (H) Finally, reverse sputtering is performed with the bias voltage applied to the substrate, and the dielectric material on the resin pattern 28a is removed by sputtering.

(I) The resin pattern 28a is removed. As a method for removing the resin pattern 28a, for example, CAROS cleaning (cleaning with a mixed solution of sulfuric acid and hydrogen peroxide solution) is performed, and the resin pattern 28a that is an organic substance is dissolved and removed.
As a result, a phase plate having a fine concavo-convex structure in which the ridges 32 of the dielectric material 30 are formed on the substrate 26 is completed. The pattern made of the dielectric material 30 is a ridge 32 extending in a direction perpendicular to the paper surface, and the surface of the substrate 26 and the ridge 32 constitute a fine concavo-convex structure.

(Example 2)
As Example 2, a method of manufacturing an optical element in which silsesquioxane is used as a resin and silsesquioxane is present in a gap of a fine concavo-convex structure having a rectangular cross section made of a dielectric will be described.
This example is the same as Example 1 in that silsesquioxane is used for the resin and the steps of FIGS. 3A to 3H are performed. Then, silsesquioxane is left by not performing step (I).

(Example 3)
FIG. 4 shows an embodiment in which fine concavo-convex patterns made of ridges 30a and 30b made of a dielectric material are formed on both surfaces of the substrate 26. FIG. In the case of forming fine concavo-convex patterns composed of the ridges 30a and 30b on both surfaces of the substrate 26, a pattern made of a dielectric material is formed on each surface of the substrate 26 by exactly the same method as in FIG.
If the phase difference of the fine uneven structure on one side of the obtained phase plate is λ / 4, the phase plate having the fine uneven structure on both surfaces as shown in FIG. 5 has a double phase difference of λ / 2. It will have.

The manufactured phase plate is manufactured by using the above-described manufacturing method using TiO ₂ (refractive index: 2.25) as a dielectric material on both sides of a parallel flat quartz glass substrate having a thickness of 1.0 mm and a refractive index of 1.45. Thus, a fine concavo-convex structure having a rectangular wave cross section was formed as a subwavelength structure.

The specifications and characteristics of the manufactured phase plate are as follows.
(1) Phase plate A (phase plate equivalent to a half-wave plate for blue image light)
Fine uneven structure on the surface of the thin layer:
Pitch: P = 0.20 μm
Filling factor: f = 0.6
Land width: L = 0.120 μm
Space width: S = 0.080 μm,
Groove depth: H = 0.380 μm
Optical property range:
Use wavelength: 420-520 nm,
Retardation: 50 ± 3% (50% is phase difference: π),
Transmittance: 0.88 ± 7% (polarization component TE); 0.93 ± 7% (polarization component TM).
The groove depth H represents the depth of the concavo-convex structure on one side, and since the concavo-convex structure is formed on both sides, the groove depth becomes 2H when both sides are combined. The same applies to the following phase plates

(2) Phase plate B (a phase plate equivalent to a half-wave plate for green image light)
Fine uneven structure on the surface of the thin layer:
Pitch: P = 0.22 μm
Filling factor: f = 0.7
Land width: L = 0.154 μm,
Space width: S = 0.066 μm,
Groove depth: H = 0.543 μm
optical properties:
Use wavelength range: 520 to 620 nm,
Retardation: 50 ± 3% (50% is phase difference: π),
Transmittance: 0.88 ± 9% (polarization component TE); 0.93 ± 5% (polarization component TM).

(3) Phase plate C (phase plate equivalent to a half-wave plate for red image light)
Fine uneven structure on the surface of the thin layer:
Pitch: P = 0.30 μm
Filling factor: f = 0.5
Land width: L = 0.150 μm
Space width: S = 0.150 μm
Groove depth: H = 0.475 μm
optical properties:
Use wavelength range: 620 to 700 nm,
Retardation: 50 ± 4% (50% is phase difference: π),
Transmittance: 0.88 ± 5% (polarization component TE), 0.93 ± 4% (polarization component TM).

  FIG. 5 shows the retardation characteristics of each phase plate in this production example. It can be seen that stable retardation can be secured in each wavelength region of the three primary colors (blue: 420 to 520 nm, green: 520 to 620 nm, red: 620 to 700 nm).

Example 4
The protrusions 32 made of a dielectric material of the optical element manufactured by the manufacturing method of FIG. 3 are formed as a multilayer film structure, and the refractive index structure of the multilayer film structure is a thin film structure having an antireflection effect on the surface. There is something.

In the film forming steps (C) to (G) in FIG. 3, dielectric films having different refractive indexes are deposited to form a multilayer film structure. Here, the following multilayer film structure was manufactured by repeating the film formation process four times.
Substrate: quartz glass substrate (refractive index 1.47),
First dielectric layer: SiO ₂ (refractive index 1.45) film thickness 86 nm,
Second dielectric layer: Al ₂ O ₃ (refractive index 1.63) film thickness 77 nm,
Third dielectric layer: TiO ₂ (refractive index 2.30) film thickness 109 nm,
Fourth dielectric layer: SiO ₂ (refractive index 1.45) film thickness 86 nm,
Concave portion between ridges 32: air (refractive index 1.00)

  In this way, the ridges 32 made of a dielectric having a four-layer structure with a total film thickness of 358 nm were formed on one side of the substrate. When a multilayer film having this structure is formed on a flat surface, the reflectance becomes 0.5% or less. By producing this multilayer optical element on both surfaces of the substrate, the surface has a function of an antireflection film, and a phase plate equivalent to a half-wave plate for blue light is obtained.

(A) is a schematic cross-sectional view showing an example of an optical element to be manufactured by the method of the present invention, (C) is an enlarged cross-sectional view of a part thereof, and (C) is a cross-sectional view for explaining the operation principle of the phase plate. is there. It is process sectional drawing which shows the process of manufacturing a metal mold | die in one Example. It is process sectional drawing which shows the process of forming the fine uneven structure with a dielectric material in the Example. It is a schematic sectional drawing which shows the phase plate which formed the fine uneven structure on both surfaces of the board | substrate in another Example. It is a graph which shows the retardation characteristic of the three phase plates manufactured by this invention.

Explanation of symbols

20 Silicon Substrate 22 Electron Beam Resist 22a Resist Pattern 24 Mold 26 Product Substrate 28 Transfer Resin 28a Resin Pattern 30 Dielectric Material 32, 32a, 32b Projection by Dielectric Material

Claims (5)

A method of manufacturing an optical element, comprising the steps (A) to (C) described below, wherein an optical element in which a fine concavo-convex structure having a rectangular cross section made of a dielectric is formed on at least one surface of a substrate is formed. .
(A) a step of forming a pattern having irregularities opposite to the fine concavo-convex structure by the resin ridges arranged on the substrate surface;
(B) a film forming step of filling the concave portions of the pattern with a dielectric layer by a film forming method , including a bias plasma film forming step performed by applying a bias voltage to the substrate side in the middle thereof; The film forming step includes a substrate bias etching step of selectively removing the dielectric material formed on the convex portions of the pattern by performing reverse sputtering with a bias voltage applied to the substrate side. A film forming step of filling the concave portion of the pattern with the dielectric layer without a dielectric layer on the convex portion , and (C) a step of removing the resin.   The step (A) is a shape transfer step by an imprint method in which a resin layer is formed by applying a resin to the substrate surface, and after pre-baking, the mold having the fine uneven structure is pressed against the resin layer. The manufacturing method as described in. An optical element in which a fine concavo-convex structure having a rectangular cross section made of a dielectric is formed on at least one surface of a substrate and silsesquioxane is present in the gaps of the fine concavo-convex structure is formed by the following steps (A) and (B The manufacturing method of the optical element characterized by the above-mentioned.
(A) Silsesquioxane is applied to the substrate surface to form a silsesquioxane layer, and after pre-baking, the silsesquioxane layer is pressed against the mold having the fine concavo-convex structure by an imprint method. After performing shape transfer, the step of thermally curing the silsesquioxane to form a pattern having concavities and convexities opposite to the fine concavo-convex structure by means of the ridges of silsesquioxane, and (B) the pattern by a film forming method Including a bias plasma film forming step in which a bias voltage is applied to the substrate side in the middle, and the bias plasma film forming step includes a bias voltage on the substrate side. Including a substrate bias etching step of selectively removing the dielectric material formed on the convex portions of the pattern by performing reverse sputtering in the state of applying Then, a film forming step of filling the concave portion of the pattern with the dielectric layer in a state where the convex portion of the pattern has no dielectric layer . The process according to any one of claims 1 to 3 wherein step (B) is for forming the dielectric layer as a multilayer structure. The manufacturing method according to claim 4 , wherein the refractive index configuration of the multilayer film structure is a thin film configuration whose surface has an antireflection effect.

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