JP2010064321A - Mold and method of manufacturing optical element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain locally almost uniform UV irradiation for e.g. a UV-hardenable resin, thus enable molding an optical element having desired performance. <P>SOLUTION: A mold (1) is used to mold an optical element (10) by irradiating a light-energy-hardenable resin (12) with light and formed of a base material having permeability to used light (Lu) and contains a plurality of light-scattering pieces (1a) which are arranged in the mold and scatter incident light. The light-scattering pieces have refractive indices different from that of the base material and a granular form and are distributed in the vicinity of the surface 1b having a fine structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mold used to mold an optical element by irradiating light onto a light energy curable resin, and a method of manufacturing an optical element using the mold.

  When an optical element such as a diffraction grating is molded using a mold, the shape of the mold may affect the cured state of the molded product. For example, a UV curable (ultraviolet curable) resin (hereinafter also simply referred to as “UV resin”) is sandwiched between a metal mold and a base material (substrate) of an optical element, and UV is applied from the substrate side. When cured by irradiating light (ultraviolet rays), the mold surface acts as a mirror or creates a shadow part. As a result, the curing process of the UV resin in the lattice shape becomes non-uniform.

  In addition, when an optical element is molded using a light transmissive mold made of, for example, quartz glass, the UV light is refracted and diffracted by the mold, and the irradiation of the UV light on the resin becomes nonuniform. Although not as high as metal molds with high reflectivity, UV light irradiation is uneven due to Fresnel reflection and periodic phase difference at the interface due to the difference in refractive index between resin and transmissive mold. Arise. Here, the irradiation non-uniformity of the UV light is not a non-uniformity as a macro distribution but a micro (local) non-uniformity seen inside one period of the lattice structure.

  Irradiation non-uniformity as a macro distribution can be solved by an existing technique for adjusting the characteristics of the light source. As an example, UV light in a macro sense is obtained by interposing a diffusion plate in the optical path between the UV light source and the mold or between the UV light source and the optical element substrate, that is, between the UV resin and the light source. There has been proposed a technique for improving the irradiation uniformity (see, for example, Patent Document 1).

JP 2005-173057 A

  Certainly, the light from the light source is ideally diffused by the action of a diffuser plate, etc., so that the light incident on the object such as the base material or mold of the optical element has a certain degree of angular distribution. Thus, substantially uniform light irradiation, that is, macro irradiation uniformity can be achieved. However, even if the light from the light source is ideally diffused, the local irradiation nonuniformity seen inside one period of the lattice structure cannot be eliminated.

  This is because the diffusing plate is arranged at some distance from the UV resin to be cured, and thus far away from the size of the diffractive structure. As a result, the angle of UV light incident on an object such as a substrate or a mold cannot be distributed sufficiently large, and local irradiation unevenness of UV light occurs.

  Thus, in the prior art, local non-uniformity is likely to occur in the irradiation of UV light to the UV curable resin. For this reason, local non-uniformity in resin characteristics occurs at the tip of the microstructure of the optical element, and as a result, it is difficult to manufacture an optical element having desired performance.

  The present invention has been made in view of the above-described problems. For example, a UV curable resin can be locally and substantially uniformly irradiated with UV light, and an optical element having a desired performance is molded. The purpose is to provide a mold that can be used.

In order to solve the above problems, in the first embodiment of the present invention, in a mold used to mold an optical element by irradiating light to a light energy curable resin,
Provided is a mold characterized in that it includes a plurality of light scatterers that are formed of a base material that is transparent to the light used, and that are distributed in the interior to scatter incident light.

In the second embodiment of the present invention, in a manufacturing method for manufacturing an optical element using the mold of the first embodiment,
Provided is a manufacturing method characterized in that a light energy curable resin is disposed so as to be in contact with the surface of the mold, and light is irradiated from at least one of the mold side and the resin side. .

  The mold of the present invention used to mold an optical element by irradiating light onto a light energy curable resin is formed of a base material that is transparent to the light used, and is distributed and arranged inside the mold. It includes a plurality of light scatterers that scatter light. In this configuration, since the mold itself including a plurality of light scatterers serves as a diffusion plate, light is irradiated almost uniformly to every corner of the resin fine structure in contact with the surface of the mold. As a result, in the mold of the present invention, for example, UV irradiation can be performed evenly locally on a UV curable resin, and an optical element having desired performance can be molded.

  The basic concept of the present invention will be described below prior to describing specific embodiments. As described above, in the prior art, local non-uniformity is likely to occur in the irradiation of UV light with respect to the UV curable resin. This local non-uniformity is caused by the refractive index and internal stress of the cured resin. Affect. The UV curable resin starts curing of surrounding monomers by irradiating the contained curing initiator with UV light having a certain energy amount or more. If the UV light applied to the resin has a local distribution, a local distribution also occurs in the curing order of the resin according to the local distribution.

  On the other hand, it is known that curing shrinkage occurs in a UV curable resin, and the refractive index increases due to the curing shrinkage. Further, when curing shrinkage is incomplete for some reason, internal stress is accumulated in the cured resin, and the refractive index varies depending on the internal stress. That is, the local irradiation non-uniformity of the UV light causes internal stress to accumulate in the cured resin and makes the refractive index of the cured resin locally non-uniform. For example, it can be easily predicted that the phase distribution of the diffracted light will be different from the designed phase distribution if there is refractive index unevenness within the same period in one period of the diffraction grating as an optical element.

  In the present invention, for example, a mold is formed of a material (matrix) that is transparent to use light such as UV light, and a plurality of light scatterers that scatter incident light are distributed therein. Here, the light scatterer has, for example, a granular form and a refractive index different from that of the base material. As a result, in the mold of the present invention, the mold itself including a plurality of light scatterers serves as a diffusion plate, and UV light is uniformly and uniformly irradiated to every corner of the resin fine structure in contact with the mold surface. Become.

  Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a configuration of a mold according to an embodiment of the present invention and a method for manufacturing an optical element using the mold. In this embodiment, as an example, the present invention is applied to a mold and a manufacturing method for forming a hybrid diffraction grating by irradiating a UV curable (ultraviolet curable) resin with UV light (ultraviolet light). ing.

  Referring to FIG. 1, the mold 1 of the present embodiment is formed of an optical material (base material) that is transparent to UV light Lu that is used light. A large number of light scatterers 1 a that scatter incident light are distributed in the mold 1. The light scatterer 1a has a granular form and a refractive index different from that of the base material.

  On the surface 1 b of the mold 1, a fine pattern corresponding to the diffractive optical surface of the hybrid diffraction grating 10 to be manufactured is formed. However, in FIG. 1, the shape of the surface 1b is shown in a simplified manner for the sake of clarity of the drawing. The light scatterers 1a are arranged in the mold 1 in accordance with a required distribution. In particular, it is important that the light scatterers 1a are distributed in a region near the surface 1b having a fine structure.

  In the manufacturing method of the present embodiment, as shown in FIG. 1, a UV curable resin 12 is sandwiched between a light-transmitting base material 11 such as a quartz glass substrate and the surface 1b of the mold 1, and a mold is formed. 1 is irradiated with UV light Lu from the base surface 1c side and the substrate 11 side. In this case, as shown in FIG. 2, the UV light Lu irradiated from the base 1c (not shown in FIG. 2) side of the mold 1 is scattered by the light scatterers 1a distributed inside the mold 1. The light is emitted almost uniformly from the interface between the mold 1 and the resin 12 toward the resin 12.

  Further, as shown in FIG. 3, the UV light Lu irradiated from the side of the base material 11 (not shown in FIG. 2) is transmitted through the base material 11, the resin 12, and the interface between the resin 12 and the mold 1. , Enters the inside of the mold 1. The UV light Lu incident on the inside of the mold 1 is scattered by the light scatterer 1a distributed in the region in the vicinity of the surface 1b inside the mold 1 and then toward the resin 12 from the interface between the mold 1 and the resin 12. It is emitted almost uniformly.

  As described above, in the present embodiment, the mold 1 is formed of a material that is transparent to the UV light that is the used light, and incident light is emitted into the mold 1 (particularly in a region near the surface 1b having a fine structure). A number of light scatterers 1a to be scattered are distributed. Therefore, the mold 1 of this embodiment has a function of scattering UV light in the vicinity of the fine structure of the surface 1b.

  Thus, in this embodiment, the mold 1 including a large number of light scatterers 1a serves as a diffusion plate, and UV light is uniformly irradiated to every corner of the fine structure of the resin 12 in contact with the surface 1b of the mold 1. . As a result, in the mold of the present embodiment and the manufacturing method using the mold, a hybrid diffraction grating that achieves substantially uniform UV light irradiation locally on the UV curable resin 12 and has desired performance. 10 (11, 12) can be molded.

  Specifically, in the present embodiment, the UV resin 12 in the microstructure of the surface 1b of the mold 1 can be irradiated with the UV light Lu almost uniformly, so that the cured resin constituting the hybrid diffraction grating 10 is cured. The uniformity of the refractive index of 12 and the internal stress can be improved both locally and locally.

  Hereinafter, the operational effects of the present embodiment will be verified according to numerical examples. In each numerical example, an RCWA is used under the condition that a UV resin having a refractive index of 1.53 is used, a plane wave of UV light having a wavelength of 350 nm is vertically incident, and a blazed grating having a pitch of 20 μm and a height of 20 μm is formed. Analysis by the method was performed. The RCWA method will be briefly described below.

  The RCWA (Rigorous Coupled Wave Analysis) method is one of strict electromagnetic field analysis methods for periodic structures. The RCWA method is a calculation method for calculating a diffraction efficiency by expressing a dielectric constant distribution by Fourier series expansion, obtaining a coupling equation with an electromagnetic field, and solving this numerically under boundary conditions. The periodic structure is divided into multiple layers in the height direction, and the electromagnetic field of each layer is handled by developing it in the eigenmode of the Maxwell equation. Since the electromagnetic field is analyzed in three dimensions, the parameters used are the dimensional components (Ex, Ey, Ez, Hx, Hy, Hz) of the electric field E and the magnetic field H.

When linearly polarized light is considered for simplification, since the electric field E and the magnetic field H are orthogonal, only the following components are displayed. However, the diffraction grating surface is in the XY plane. The groove is parallel to the Y axis. Light incident direction is Z direction.
TE mode (polarization where the electric field is parallel to the groove) Hx, Ey, Hz
TM mode (electric field perpendicular to groove) Ex, Hy, Ez

  Here, what is required is not the diffraction efficiency but the electromagnetic field distribution in the near field. In the RCWA method, the electromagnetic field distribution at each location can also be calculated. Specifically, it is examined whether there is a bias in the electromagnetic field intensity distribution when UV light is irradiated in a UV curable resin sandwiched between mold shapes. Therefore, a plane wave having a wavelength of 350 nm in TE mode is used as incident light, and an intensity map of Hx, Ey, Hz is obtained as a calculation result. In order to determine whether the intensity distribution is uneven, one of Hx, Ey, and Hz may be viewed.

  4 to 6 below, the intensity distribution of the magnetic field component Hx of light is shown in the form of mapping data as a result of numerical simulation. In FIGS. 4-6, the intensity | strength of a dark part is high. Accordingly, it can be expected that the resin is cured in advance in a dark portion, that is, in a region where the electromagnetic field is strong.

  4 and 5 are diagrams showing the intensity distribution of the magnetic field component Hx of the UV light when the UV resin is cured in the first comparative example and the second comparative example. FIG. 6 is a diagram illustrating the intensity distribution of the magnetic field component Hx of the UV light when the UV resin is cured in the present embodiment. 7 and 8 are diagrams showing the relationship between the X-direction position at Z = 10 μm and the magnetic field component Hx of the UV light in the first comparative example and the second comparative example. FIG. 9 is a diagram illustrating the relationship between the position in the X direction at Z = 10 μm and the magnetic field component Hx of the UV light in the present embodiment. That is, FIGS. 7 to 9 show the amplitude (power) of the magnetic field component Hx of the UV light at each position of Z = 10 μm and X = −10 μm to +10 μm.

  In the first comparative example of FIG. 4, a mold 41 made of a metal having a complex refractive index with a refractive index (n) of 1.6 and an extinction coefficient (k) of 2.2 is used. A plane wave of UV light is vertically incident from the side. In the second comparative example of FIG. 5, a plane wave of UV light is vertically incident from the side of the mold 51 using a mold 51 formed of a light transmissive material having a refractive index of 1.49. In the present embodiment of FIG. 6, a spherical light scatterer 1a formed of a light-transmitting material (base material) having a refractive index of 1.49, having a refractive index of 2.0 and a diameter of 0.2 μm is distributed. Using the arranged mold 1, a plane wave of UV light is vertically incident from the mold 1 side.

  Focusing on the vicinity of the edge of the formed diffraction grating, in the first comparative example and the second comparative example, a region having a small magnetic field component Hx exists particularly in the range of X = 0 μm to −1 μm, and the resin is refracted after curing. It is expected to produce a rate distribution. On the other hand, in this embodiment, although there is a portion where the magnetic field component Hx is locally reduced, the interval is so small as to be negligible as compared with the wavelength of light. Even if a refractive index distribution corresponding to the magnitude of the component Hx is generated, it responds to the light as having an average refractive index. That is, the distribution of the magnetic field component Hx in the present embodiment is substantially negligible.

  Furthermore, the simulation of the present embodiment is only a calculation in one cross section in the Y direction (direction perpendicular to the paper surface of FIG. 6). Actually, since the light scatterers inside the mold are randomly distributed in the Y direction, the distribution of the magnetic field component Hx formed in the resin is also random, averaged in the Y direction, and substantially uniform. . On the other hand, in the first comparative example and the second comparative example, since the light scatterer is not included in the mold, the distribution of the magnetic field component Hx is uniform in the Y direction, and from the edge over the entire length of the grating edge. In the region of 1 μm, the irradiation light quantity is always insufficient.

  In the above-described embodiment, the UV curable resin 12 is sandwiched between the base material 11 and the surface 1b of the mold 1, and the UV light Lu is emitted from the base 1c side of the mold 1 and the base material 11 side. Irradiating. However, the present invention is not limited to this. By irradiating UV light from at least one of the mold side and the substrate side, the same effects as those of the above-described embodiment can be obtained. However, in the case of using a base material that is not transmissive to the used light, the UV light is irradiated only from the mold side. Moreover, when irradiating UV light from either side using a light-transmitting substrate, it is preferable to irradiate UV light from the mold side.

  Further, in the above-described embodiment, the hybrid diffractive grating is formed by irradiating the UV curable resin with UV light. However, the present invention is not limited to the UV curable resin and the hybrid diffraction grating, and other appropriate optical elements can be formed by irradiating the light energy curable resin with necessary light. When molding a non-hybrid optical element that does not have a substrate, a light energy curable resin is disposed so as to contact the surface of the mold, and at least one of the mold side and the resin side is arranged. It is sufficient to irradiate light from.

It is a figure which shows roughly the structure of the type | mold concerning embodiment of this invention, and the method of manufacturing an optical element using this type | mold. It is a figure which shows a mode that UV light irradiated from the type | mold side is radiate | emitted from the interface toward resin substantially uniformly. It is a figure which shows a mode that the UV light irradiated from the base-material side is radiate | emitted substantially uniformly toward the resin from the interface. It is a figure which shows intensity distribution of the magnetic field component Hx of UV light when UV resin hardens | cures in a 1st comparative example. It is a figure which shows intensity distribution of the magnetic field component Hx of UV light when UV resin hardens | cures in a 2nd comparative example. It is a figure which shows intensity distribution of the magnetic field component Hx of UV light when UV resin hardens | cures in a present Example. It is a figure which shows the relationship between the X direction position in Z = 10micrometer of a 1st comparative example, and the magnetic field component Hx of UV light. It is a figure which shows the relationship between the X direction position in Z = 10micrometer of 2nd comparative example, and the magnetic field component Hx of UV light. It is a figure which shows the relationship between the X direction position in Z = 10 micrometer of a present Example, and the magnetic field component Hx of UV light.

Explanation of symbols

1 type 1a light scatterer 1b type surface 1c type basal plane 10 hybrid diffraction grating 11 diffraction grating substrate 12 UV resin Lu UV light

Claims (8)

In a mold used to mold an optical element by irradiating light onto a light energy curable resin,
A mold comprising a plurality of light scatterers that are formed of a base material that is transmissive to the light used, and that are distributed in the interior to scatter incident light. The mold according to claim 1, wherein the light scatterer has a refractive index different from that of the base material. The mold according to claim 1, wherein the light scatterer has a granular form. The mold according to any one of claims 1 to 3, wherein the plurality of light scatterers are distributed in a region in the vicinity of a surface having a fine structure. The mold according to any one of claims 1 to 4, wherein the base material is permeable to ultraviolet rays. In the manufacturing method which manufactures an optical element using the type | mold of any one of Claims 1 thru | or 5,
A manufacturing method, wherein a light energy curable resin is disposed so as to be in contact with the surface of the mold, and light is irradiated from at least one of the mold side and the resin side. The light is irradiated from at least one of the mold side and the substrate side with the resin sandwiched between the base of the optical element and the surface of the mold. 6. The production method according to 6. The manufacturing method according to claim 6, wherein light is irradiated from the mold side.

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