JP2002080242A - Method of manufacturing optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical lens for irradiating a recording layer of an optical disc. SOLUTION: This method comprises forming a photo-converging means on one surface of a substrate 1 made from an optical material by dry-etching using as an etching gas a mixed gas of a fluorocarbon gas and at least a gas selected from the group consisting of oxygen gas, Ar gas and He gas. For example, after forming a masking piece corresponding with the shape of an optical lens on the substrate made from an optical material, deforming the shape of the masking piece to shrink in its surface area by thermal treatment, transcribing a photo-converging means corresponding with the shape of the mask on the substrate by dry-etching to form a small hemisphere lens 4.

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 / reproducing apparatus for recording / reproducing information signals on / from an optical recording medium such as an optical disk.

[0002]

2. Description of the Related Art In recent years, there has been proposed an optical disk apparatus which realizes high-density recording by increasing an NA by arranging an optical system on an optical recording layer side of an optical disk.

This optical disk device uses an optical element having two lenses as light converging means as disclosed in, for example, JP-A-10-123410, as an objective lens.

The above optical element is a lens on the optical disk side of the two lenses (hereinafter, the lens on the optical disk side is called a front lens, and the other lens is called a rear lens).
Is composed of a so-called hemispherical lens.

The numerical aperture NA of the optical element is determined by a stop (light transmission hole) provided before the light is emitted from the light source and enters the optical element.

In the optical element having the above structure, recording light and reproduction light are converged by the rear lens and the front lens.
Irradiates the optical recording layer of the optical disc.

[0007]

By the way, the above optical element (optical lens) includes a plastic lens formed by injection molding, a glass lens formed by a glass molding method, and a glass lens formed by polishing. It is typical.

However, all of these lenses have a problem that it is not easy to reduce the radius of curvature, and consequently it is not easy to manufacture a small-diameter optical lens.

There is also a proposal to manufacture a lens having a continuous curved surface by applying a method for manufacturing a Fresnel lens.
It is difficult to produce a highly accurate lens.

The present invention has been proposed in view of such conventional circumstances, and has as its object to provide a method for manufacturing an optical element capable of accurately manufacturing a small optical lens having a large radius of curvature. I do.

[0011]

In order to achieve the above-mentioned object, a method of manufacturing an optical element according to the present invention is directed to a method of forming an optical element in which light converging means is formed on one surface of a substrate made of an optical material by dry etching. In the manufacturing method, a mixed gas of at least one selected from oxygen gas, Ar gas, and He gas and a fluorocarbon gas is used as an etching gas.

By using dry etching, an optical lens having a small size and a large radius of curvature can be easily manufactured.

For example, after a mask material corresponding to the shape of an optical lens is formed on a substrate made of an optical material, heat treatment is performed to deform the shape of the mask material so as to reduce the surface area, and the mask is formed by dry etching. By transferring the light converging means having a shape corresponding to the shape onto the substrate, a small hemispherical lens is formed.

At this time, by using a mixed gas of at least one selected from oxygen gas, Ar gas and He gas and a fluorocarbon gas as an etching gas,
The surface properties of the formed optical lens are greatly improved.

[0015]

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.
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 forming a shape corresponding to the shape of the mask material on the optical material. In this example, a step of forming a shape corresponding to the shape of the mask material on the optical material by using a dry etching method.

FIG. 1 shows the above step (a). First, a photosensitive material is applied on a substrate 1 made of an optical material by a spin coating method or the like to form a mask material layer 2.

Next, as shown in FIG. 2, the mask material layer 2 is patterned by exposure and development to form a mask 3 corresponding to each lens.

Then, as shown in FIG. 3, a heat treatment is performed to deform the mask material so that the surface area of the mask material is reduced, thereby deforming the mask 3 into a shape having an optically gentle curved surface.

Here, when an arbitrary photosensitive material is used for 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 the heat treatment was conducted at a heat treatment temperature of 110 to 150 ° C., when the heat treatment was performed at a temperature of 200 ° C. or more, any of the resist materials deteriorated (so-called burn-in). )
Has occurred. If the alteration occurs, the etching rate of 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.

According to the experimental results, the condition that the mask material is rounded by the heat treatment to obtain an optically smooth surface is that the glass transition point Tg of the mask material is lower than the heat treatment temperature. . Further, when the mask is to be formed into an optical lens shape by a method such as dry etching, the mask material after the heat treatment must not be altered as described above. In addition, a condition that the temperature is such that the mask material is not deteriorated is required.

When plating is formed on a mask material and the plating is used as a mold (when forming a replica)
In, because the etching of the mask material is not performed,
Although this condition is not always necessary for the above-mentioned reason, even in the case of forming a replica, when the mask material is deteriorated by the heat treatment, the mask material surface is often roughened. ,
The temperature must not change the quality of the mask material. Is a desirable condition even when such a replica is formed.

Furthermore, if the mask is deformed while holding the substrate on which the mask is formed, the reproducibility of the process becomes difficult, and if the mask is deformed during the dry etching process, the process is reproducible. It is desirable that the glass transition point Tg of the mask material be higher than the storage temperature (room temperature) or the processing temperature (near room temperature) because the glass material becomes difficult to operate.

Here, generally, the glass transition point Tg is a temperature at which a material is in a glassy state, that is, a temperature indicating a boundary where a material does not have a fixed structure and is capable of flowing. 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, after the mask 3 is deformed into a round shape, a shape corresponding to the shape of the mask 3 is formed on the optical material as shown in FIG. Specifically, a shape corresponding to the shape of the mask 3 is formed on the optical material by using a dry etching method. This becomes the hemispherical lens 4.

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

It is important to select an etching gas, and a mixed gas of at least one selected from oxygen gas, Ar gas and He gas and a fluorocarbon gas is used.

Here, CHF is used as the fluorocarbon gas.
_Three , CH_TwoF_Two, CF_Four , C_TwoF₆, C _ThreeF₈, C_FourF₈, C_Five
F₈And the like.

As a specific combination, C ₃ F ₈ + A
r, C ₃ F ₈ + O ₂ , C ₃ F ₈ + Ar + O ₂ , C ₃ F ₈ + H
_{e, C 3 F 8 + Ar} + He, C 3 F 8 + He + O 2, C 3 F 8
+ Ar + He + O _{2 and the} like.

In the above mixed gas, Ar has the effect of improving the surface properties by physical etching. Oxygen gas is
It has the function of removing carbonized products and adjusting the selectivity.
He has a function of adjusting a gas pressure for maintaining a discharge and a light physical etching.

In any case, a lens having a smooth surface property is formed by using these mixed gases.

FIG. 5 shows the surface properties of a lens manufactured by using C ₃ F ₈ + C ₂ F ₆ + O ₂ as an etching gas, and FIG. 6 shows the etching of C ₃ F ₈ + C ₂ F ₆ . It shows the surface properties of a lens manufactured using a gas.

It can be seen that the surface properties are greatly improved by using oxygen gas together. With fluorocarbon gas alone, fine residues remain on the surface.

Finally, the optical lens is adjusted to a predetermined thickness by a polishing process to complete the optical lens.

In this example, a fused quartz substrate was used as the glass material of the substrate 1, a photosensitive material was applied to a thickness of about 20 μm, and a circular pattern of about 120 μm was formed by exposure and development steps. This was deformed by a heat treatment temperature of 150 ° C., and an optical lens was manufactured by high-density plasma etching (high-speed etching by NLD plasma) using magnetic neutral discharge.

The manufactured optical lens is an optical lens having an optically smooth curved surface, an extremely small diameter optical lens having an optical lens portion having a diameter of about 120 μm, and an optical lens having a convexity of about 30 μm. It is a high NA optical lens having a part height.

Further, since the position where the substrate 1 and the mask 3 are in contact does not move even after the heat treatment step, 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 optical lens is formed at an extremely high precision position. Further, the height of the optical lens is defined by the thickness of the mask 3.

In the optical lens manufactured as described above, since it is defined by the photomask used when exposing the photosensitive material, a multi-lens (or lens) in which a plurality of optical lenses are formed on the same substrate is used. In the case of (array), the position of the optical lens is formed at a position with high precision in both the position as a single unit and the mutual position of the lenses. Further, the manufactured optical lens can form an optical lens having a larger NA than an optical lens formed by a conventional diffusion process, and thus has a wide range of application.

[0044]

As is clear from the above description, according to the method of manufacturing an optical element according to the present invention, an optical lens having a small radius and a large radius of curvature can be manufactured with high accuracy.

[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 showing a mask forming step.

FIG. 3 is a schematic view showing a step of deforming a mask by heat treatment.

FIG. 4 is a schematic view showing a lens forming step 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 schematic diagram showing the surface properties of a lens that has been dry-etched using only a fluorocarbon gas.

[Explanation of symbols]

 1 substrate, 3 masks, 4 hemispherical lenses

Claims (3)

[Claims] 1. A method of manufacturing an optical element in which light converging means is formed on one surface of a substrate made of an optical material by dry etching, wherein at least one selected from oxygen gas, Ar gas, and He gas is used as an etching gas. A method for producing an optical element, comprising using a mixed gas with a carbonized gas. 2. After forming a mask material corresponding to the shape of an optical lens on a substrate made of an optical material, heat treatment is performed to deform the shape of the mask material so as to reduce the surface area, and the mask is formed by dry etching. 2. The method for manufacturing an optical element according to claim 1, wherein a light converging means having a shape corresponding to the shape is transferred and formed on the substrate. 3. The method according to claim 2, wherein the temperature of the heat treatment is higher than the glass transition temperature of the mask material and lower than the carbonization temperature.