JP2002321941A - Method for producing optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely produce a small-sized optical lens having the large radius of curvature. SOLUTION: A mask 3 is formed on the substrate 1 made of an optical material, coping with the shape of a semi-spherical lens 4. The semi-spherical lens 4 corresponding to the shape of the mask 3 is formed through dry etching. For example, a mask material layer 2 is formed on the substrate 1 made of the optical material and the mask material layer 2 is formed into the mask 3 of a cylindrical shape, coping with the bore of the semi-spherical lens 4. The shape of the mask 3 is deformed by heat treatment so as to have its small surface area. Then, the semi-spherical lens 4 is transferred to the substrate 1 almost in accordance with the shape of the mask 3 by varying the ratio of an etching speed to the substrate 1 and an etching speed to the mask 3 during dry etching. So that the small-sized semi-spherical lens 4 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical element used in a recording and / or reproducing apparatus for recording and / or reproducing an information signal on an optical recording medium such as an optical disk.

[0002]

2. Description of the Related Art Hitherto, as a method of forming a micro optical element on a substrate surface made of an optical material, a method using thermal deformation of a photosensitive resin has been proposed. As an apparatus for forming a micro optical element by such a method, a photolithography apparatus in a usual semiconductor element manufacturing is used.
As an optical element formed on the substrate surface, a microlens formed in a minute convex lens is applied to an optical pickup such as an optical disk device, so that the optical pickup is reduced in size and weight, and further, the optical disk device is reduced in size and weight. It is contributing to the development. Also, a micro lens array in which convex lenses are formed in an array form an image pickup element for image input,
It is applied to an optical element for connecting an optical fiber and an optical element.

An outline of a method for forming such a micro lens by thermal deformation is as follows.

[0004] First, a photosensitive resin is applied to the substrate surface so as to have a constant thickness, and the same diameter as the microlens is formed by a usual photolithography method using a mask having a pattern shape of the microlens to be formed. The photosensitive resin is patterned into a cylindrical shape having

[0005] Next, the photosensitive resin patterned into the cylindrical shape is heated to a temperature at which the photosensitive resin has fluidity, the temperature is maintained for a certain period of time, and the cylindrical photosensitive resin is formed by surface tension. The microlens is obtained by deforming the conductive resin into a convex curved surface shape.

The details of the method of manufacturing such a micro lens by thermal deformation of a photosensitive resin are described in British Cr
Own published journal Measurement Science Technology. Vo
l.1 ((1999), pp. 759-766), "The manufacture of microlenses by me
lting phoenix ", D. Daly et al.

According to this method, a microlens having a substantially spherical shape can be formed on a substrate by appropriately selecting the photosensitive resin and the conditions of the thermal deformation step. Also, by using such a method, it is possible to improve the surface accuracy of the microlens to correspond to a light source having a short wavelength such as a blue laser and to achieve a high NA, and to achieve a high recording density in an optical disc device or the like. Is expected.

[0008]

The principle of forming a curved surface of a photosensitive resin in the above method is as follows.
Because it is due to the surface tension of the fluidized photosensitive resin, when the desired microlens diameter becomes large,
As the weight of the photosensitive resin increases, the shape deformation of the photosensitive resin due to gravity becomes remarkable. As a result, the microlens manufactured using the photosensitive resin as a mask has a shape shifted from an ideal spherical surface by transferring the shape of the photosensitive resin, and the surface accuracy of the microlens decreases, In particular, there is a problem that this microlens cannot be used in an optical system at a short wavelength such as a blue laser.

There is another problem that it is difficult to achieve a high recording density in an optical disk device manufactured using such a microlens.

Therefore, the present invention has been made in view of the above-described problem, and as described above, even if the shape of the photosensitive resin deviates from the ideal spherical surface, the etching is performed so that the shape of the microlens approaches the ideal spherical surface. The purpose is to adjust the conditions.

[0011]

In order to achieve the above-mentioned object, a method of manufacturing an optical element according to the present invention comprises forming a mask material corresponding to the shape of a light converging means on a substrate made of an optical material, In a method for manufacturing an optical element in which a light converging means is formed by etching, a ratio between an etching rate for a substrate and an etching rate for a mask material is changed.

When the shape of the mask material is not an ideal spherical surface, dry etching is performed by changing the ratio of the etching rate with respect to the substrate to the etching rate with respect to the mask material, that is, by changing the etching selectivity. A lens can be made.

At this time, at least one of oxygen gas and Ar gas is used as an etching gas.
It is preferable to change the above-mentioned etching selectivity by controlling the flow rate of these gases using more than one kind of fluorocarbon gas.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an optical element to which the present invention is applied will be described with reference to the drawings.

The outline of the manufacturing process of the optical element is shown in FIGS.
It is as shown in FIG.

The following four steps are the main steps in the manufacturing process of the optical element. (A) arranging a material to be a mask material on a substrate; That is, when a photosensitive material is used as a mask material, a step of applying a predetermined thickness by a spin coating method or the like. (B) a step of patterning the mask material; In the case where a photosensitive material is used as the mask material, an exposure and development step. (C) a step of deforming the mask material so that the surface area of the mask material is reduced by heat treatment, and deforming the mask material into a shape having a gentle optically curved surface. (D) a step of transferring a shape corresponding to the shape of the mask material to the optical material. In this example, a step of transferring a shape corresponding to the shape of the mask material to the optical material using a dry etching method.

First, in the step (a), as shown in FIG. 1, a photosensitive material is applied to a substrate 1 made of an optical material by a spin coating method or the like so as to have a predetermined thickness.
The mask material layer 2 is formed.

Next, in the step (b), as shown in FIG. 2, the mask material layer 2 is patterned by exposure and development, and the mask 3 is formed into a cylindrical shape having a size corresponding to the aperture of the optical lens to be manufactured. Form.

Next, in the step (c), as shown in FIG. 3, a heat treatment is applied to the substrate 1 and the mask 3 to deform the mask 3 so that the surface area of the mask 3 is reduced.
Is deformed into a shape having an optically gentle curved surface.

When an arbitrary photosensitive material is used as the mask material, a deformation phenomenon such that the surface area of the mask material is reduced by heat treatment does not necessarily occur, and an optically smooth curved surface is not necessarily obtained.

For example, when a heat treatment is performed at a temperature of 200 ° C. or higher, a phenomenon (so-called burn-in) occurs in any of the photosensitive materials to deteriorate. If the deterioration occurs, the etching rate with respect to the mask material becomes non-uniform. Therefore, when trying to obtain a shape corresponding to the shape of the mask material in the optical material, the shape may be disturbed. There is.

Then, when the heat treatment temperature was examined in the range of 110 to 150 ° C., a deformation phenomenon in which the surface area of the mask material was reduced occurred without causing the deterioration of the mask material, and the optical material was smooth. A curved surface was obtained.

From the experimental results, it can be mentioned that the glass material has a glass transition point Tg lower than the heat treatment temperature as a condition under which the mask material is rounded by heat treatment to obtain an optically smooth curved surface. . further,
When the shape of the mask 3 is to be transferred to the optical material by a method such as dry etching, it is necessary that the mask material after the heat treatment is not deteriorated as described above. It is necessary that the temperature be such that the material does not deteriorate.

Further, if the mask 3 is deformed while holding the substrate 1 on which the mask 3 is formed,
Since the reproducibility of the process is not easy, and if the mask 3 is deformed during the dry etching process, the reproducibility of the process is not easy, the glass transition point Tg of the mask material is determined by the storage temperature (room temperature) or It is desirable that the temperature be higher than the processing temperature (around room temperature).

Here, generally, the glass transition point Tg is a temperature at which the material is in a glassy state, that is, a temperature indicating a boundary where a material does not have a fixed structure and is in a flowable state. Considering this, it is desirable that the heat treatment temperature be a temperature higher than the glass transition point Tg with a margin. That is, in order to deform the mask material by heat treatment so as to reduce its surface area (to make the mask material flowable by heat treatment and to deform the mask material by the surface tension of the mask material), the heat treatment temperature is set to the glass transition temperature. It is desirable that the temperature is several tens degrees Celsius higher than the point Tg.

More specifically, by setting the heat treatment temperature to be higher than the glass transition point Tg by about 40 ° C. or more, the mask material can be deformed in a round within one hour. be able to.

Further, from the same viewpoint, the glass transition point T
In the relationship between g and the storage temperature or the processing temperature, the difference between the storage temperature or the processing temperature and the glass transition point Tg is:
The temperature may be within several tens of degrees Celsius.

As described above, the mask 3 is deformed into a round shape.

Next, in the step (d), as shown in FIG. 4, a shape corresponding to the shape of the mask 3 is transferred to an optical material. Specifically, the mask 3 is formed using a dry etching method.
Is transferred to the optical material. This is,
As shown in FIG. 5, a hemispherical lens 4 having a smooth curved surface
Becomes

In this dry etching, it is preferable to employ high-density plasma etching (high-speed etching by NLD plasma) using magnetic neutral discharge.

Here, when the hemispherical lens 4 is manufactured with a lens diameter of 0.9 mm, the deviation from the ideal spherical surface when the shape of the mask 3 is rounded as described above is shown as a graph in FIG. As shown in this graph, the shape of the mask 3 has a deviation from the ideal spherical surface at a portion of about 0.2 to 0.4 mm from the center of the lens. Such a mask 3
When dry etching is performed by using the method, the shape of the hemispherical lens 4 to be manufactured is shifted from the ideal spherical surface similarly to the mask 3.

In the step (d) of transferring the shape of the mask 3 to the substrate 1 by high-density plasma etching, the etching rate for the substrate 1 and the mask 3 are changed by changing the selection of the etching gas and the flow rate thereof.
The deviation from the ideal spherical surface is corrected by changing the ratio of the etching rate to the ideal spherical surface, and the shape of the hemispherical lens 4 is made closer to the ideal spherical surface. If the etching selectivity is 1, the shape of the mask 3 is transferred to the substrate 1 as it is.

In the step (d), the etching gas includes, for example, two or more types of fluorocarbon gases, particularly C ₃ F ₈
And C ₄ F _8, and these flow ratios are, for example, 17
Change in steps. At this time, for example, the total flow rate is fixed at 20 sccm, and the initial condition is that the flow rate of C ₃ F ₈ is 1
0 sccm, the flow rate of C ₄ F ₈ is 10 sccm, and C
The flow rate of ₃ F ₈ is reduced by 0.5 sccm, and C ₄ F ₈
Is increased by 0.5 sccm. The amount of increase / decrease is determined by changing an ideal value according to conditions, so that the hemispherical lens 4 can have a desired ideal spherical surface.

FIG. 7 is a graph showing the deviation of the shape of the hemispherical lens 4 from the ideal spherical surface obtained under such etching conditions. From this graph, the deviation from the ideal spherical surface of the hemispherical lens 4 is clearly reduced as compared with the shape of the mask 3. As described above, by changing the etching selectivity during high-density plasma etching as described above, the shape of the hemispherical lens 4 can be approximated to an ideal spherical surface even when the diameter of the mask 3 is large enough to be deformed by gravity. Can be.

As described above, by changing the flow rate ratio between C ₃ F ₈ and C ₄ F ₈ , the etching selectivity can be changed more than 1, and the substrate 1 can be etched faster than the mask 3 at a desired time. it can. Thereby, the shape of the hemispherical lens 4 approaches the ideal spherical surface, and the optical lens has a highly accurate spherical surface. Depending on the conditions, the etching selectivity may be smaller than 1 so that the substrate 1 can be etched faster than the mask 3.

Here, other fluorocarbons which can be used as described above
The gas is CHF₃, CH₂F ₂, CF₄, C₂F
₆, C₅F₈And the like.

Further, as the above-mentioned etching gas,
It is not limited to two or more types of fluorocarbon gases, and for example, at least one of oxygen gas and Ar gas can be used. In this etching gas,
Ar gas has the effect of improving the surface properties by physical etching. Oxygen gas has a function of removing carbonized products and adjusting an etching selectivity.

In any case, by using these etching gases, a hemispherical lens 4 having a smooth surface property is formed as shown in FIG.

Finally, over-etching is performed, and the hemispherical lens 4 is adjusted to a predetermined thickness by a polishing process.
The hemispherical lens 4 is completed.

In this embodiment, a fused quartz substrate (SiO ₂ ) is used as the glass material of the substrate 1 and a positive novolak resin (PMER- manufactured by Tokyo Ohka Kogyo Co., Ltd.) is used as the photosensitive material.
Using LA900), a photosensitive material was applied to a thickness of about 100 μm, and a cylindrical pattern having a diameter of about 0.9 mm was formed by an exposure and development process. This was deformed by a heat treatment temperature of 150 ° C., and a hemispherical lens 4 was produced by high-density plasma etching (high-speed etching by NLD plasma) using magnetic neutral discharge.

The manufactured hemispherical lens 4 is an optical lens having an optically smooth curved surface and an extremely small diameter optical lens having an aperture of about 0.9 mm at the optical lens portion. The hemispherical lens 4 is a high NA optical lens having a height of a convex portion of about 150 μm.

Further, in the manufactured hemispherical lens 4, the position where the substrate 1 and the mask 3 are in contact does not move even after the heat treatment step, so that the shape of the mask 3 is defined by the boundary line.

Here, since the boundary of the mask 3 is defined by a photomask used when exposing the photosensitive material, the position of the hemispherical lens 4 is formed at an extremely high precision position. Further, the height of the hemispherical lens 4 is defined by the thickness of the mask 3.

In the hemispherical lens 4 manufactured as described above, since it is defined by a photomask used when exposing a photosensitive material, a multi-lens (or a plurality of optical lenses formed on the same substrate) is used. In the case of (lens array), the position of the optical lens is formed at a position with high precision in both the position of the single lens and the mutual position of the lenses.

Further, the hemispherical lens 4 to be manufactured has an NA
Is 0.6 or more, which can be increased as compared with an optical lens manufactured by a conventional diffusion process, so that the applicable range is wide.

The hemispherical lens 4 manufactured as described above
In the above, an optical lens having surface accuracy that can withstand an optical system for a short wavelength such as a blue laser can be provided.

The hemispherical lens 4 manufactured as described above
The diameter of the mask 3 is particularly preferably 300 μmφ to 1 mmφ. When the diameter is 300 μmφ or more, the deformation of the mask 3 due to gravity starts to appear remarkably, so that this method is particularly effective. Further, the curvature R of the hemispherical lens 4 manufactured as described above is obtained.
Is more preferably in the range of 500 μm to 300 μm.

In particular, the hemispherical lens 4 manufactured as described above
Can be used for an optical pickup device such as an optical disk, so that the optical disk device can be reduced in size, weight, and high recording density.

The method of changing the etching selectivity is not limited to the above-described method of changing the flow rate of the etching gas, and any other method may be used as long as the etching selectivity can be adjusted.

As a method for changing the etching selectivity, it is preferable to form the smoother spherical surface by changing the etching selectivity continuously rather than changing the etching selectivity stepwise.

[0051]

As is apparent from the above description, according to the method of manufacturing an optical element according to the present invention, it is possible to manufacture a small-sized optical lens having a large radius of curvature with high accuracy and to obtain an ideal spherical lens. Thus, the shape of the optical lens formed from the mask material deformed by gravity can be corrected to be an ideal spherical surface.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a process of forming an optical element in the order of processes, and illustrating a process of forming a mask material layer on a substrate.

FIG. 2 is a schematic view illustrating a mask forming step, showing a manufacturing step of an optical element in order of steps.

FIG. 3 is a schematic diagram illustrating a manufacturing process of an optical element in a process order and illustrating a process of deforming a mask by heat treatment.

FIG. 4 is a schematic diagram illustrating a manufacturing process of an optical element in a process order, and illustrating a lens forming process by dry etching.

FIG. 5 is a schematic view showing the surface properties of a lens which is dry-etched using a mixed gas of oxygen gas and fluorocarbon gas.

FIG. 6 is a graph showing a deviation from an ideal spherical surface of a mask after heat treatment.

FIG. 7 is a graph showing a deviation of a hemispherical lens from an ideal spherical surface after dry etching.

[Explanation of symbols]

 1 substrate, 3 masks, 4 hemispherical lenses

Claims (6)

[Claims] 1. A method for manufacturing an optical element, comprising: forming a mask material corresponding to the shape of a light focusing means on a substrate made of an optical material; and forming the light focusing means by dry etching. A method of manufacturing an optical element, wherein a ratio between an etching rate for the substrate and an etching rate for the mask material is changed. 2. The method for manufacturing an optical element according to claim 1, wherein the ratio between the etching rate for the substrate and the etching rate for the mask material is changed in multiple steps. 3. The method for manufacturing an optical element according to claim 1, wherein a ratio between an etching rate for said substrate and an etching rate for said mask material is continuously changed. 4. When performing dry etching, two or more types of mixed gases are used as an etching gas, and the ratio of the amount of the introduced gases is changed so that the ratio between the etching rate for the substrate and the etching rate for the mask material is changed. 2. The method for manufacturing an optical element according to claim 1, wherein 5. An oxygen gas as the etching gas,
The method for manufacturing an optical element according to claim 4, wherein at least one kind of Ar gas is used. 6. The method for manufacturing an optical element according to claim 4, wherein at least two or more types of fluorocarbon gases are used as said etching gas.