JP2002072078A - Optical device and recording and reproducing device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize precise positioning even when an error is found on the external size of a lens. SOLUTION: In the optical device having an optical lens formed by dry etching as a part of a light converging means, an alignment marker is formed around the optical lens. The alignment mark is utilized for the mutual alignment of the lenses or the alignment of the lens with other optical parts. Even when the molding error is found on the external size of the lens, the mutual alignment of the lenses or the alignment of the optical path of the lens with the center of a light transmission hole is precisely performed by the use of the alignment mark.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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.

[0003] The optical pickup of this optical disk device is used as an objective lens, for example, in Japanese Patent Application Laid-Open No. 10-12341.
An optical element having two lenses as a light converging means as shown in Japanese Patent Application Publication No. 0 is used.

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.

In the above optical pickup, the diameter of the beam focused on the optical recording medium can be reduced by increasing the numerical aperture (NA) of the objective lens.

However, in a so-called single lens,
In order to obtain a high numerical aperture, refracting power is required. When the refracting power is increased, the curvature of the objective lens decreases, and the positioning accuracy between the refracting surfaces becomes severe. Therefore, the limit of the numerical aperture NA of a single lens is about 0.6.

On the other hand, the two-unit lens composed of the above two lenses can have a large numerical aperture.

[0008]

In the above two-group lens, the distance between the first lens and the second lens is fixed, and the attitude of the second lens with respect to the first lens is also precisely determined. There is a need to.

For example, the first lens and the second lens have been molded using a mold so far, the distance between the first lens and the second lens, the second lens with respect to the first lens, Is determined based on the outer shape of each lens. Therefore, high-precision molding of the lens outer shape is required.

[0010] However, in molding using a mold, a lens can be molded only to a certain degree of accuracy, and there is a problem that it is difficult to perform precise positioning based on the outer shape.

If the positioning cannot be performed precisely, the second lens may be disposed at a different distance from the first lens with respect to the design, or the second lens may be tilted or decentered. When such a change, inclination, or eccentricity of the distance occurs, an allowable range (for example, 0. 1) required for the lens alone.
04 rms).

The present invention has been proposed in view of such conventional circumstances, and has as its object to provide an optical element which can be accurately positioned even if there is an error in the outer shape of a lens. It is another object of the present invention to provide a manufacturing method and a recording / reproducing apparatus.

[0013]

In order to achieve the above object, an optical element according to the present invention is an optical element having an optical lens formed by dry etching as a part of a light converging means. A positioning marker is formed around the periphery.

Further, the manufacturing method of the present invention is characterized in that when forming an optical lens on one surface of an optical material substrate by dry etching, an alignment marker is simultaneously formed around the optical lens. Things.

Further, the recording / reproducing apparatus of the present invention is characterized in that the above-mentioned optical element is used in at least a part of an optical system.

In the present invention, even if there is a molding error in the outer shape of the lens, the alignment of the lenses, or the optical axis of the lens and the center of the light transmitting hole, etc., is precisely performed by the positioning marker.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical element to which the present invention is applied, a method for manufacturing the same, and a recording / reproducing apparatus using the same will be described with reference to the drawings.

As shown in FIG. 1, for example, as shown in FIG. 1, the optical element of the present invention comprises a front lens 1 and a rear lens 2 having an optical axis as light converging means for converging light applied to a recording layer of an optical recording medium. They are arranged so as to match.

Here, positioning markers are formed around the lenses 1 and 2 so that they can be positioned with respect to each other.

For example, the front lens 1 has a cross-shaped positioning marker 3 as shown in FIG. 2, and the rear lens 2 has a slit corresponding to the positioning marker 3 as shown in FIG. Alignment marker 4 is formed.

Therefore, as shown in FIG. 4, for example, if the markers 3 and 4 are aligned using a CCD camera or the like so as to be coincident, the distance between the front lens 1 and the rear lens 2 is increased. , Eccentricity and so on.

Here, a slight gap is provided between the outer shape of the positioning marker 3 formed on the front lens 1 and the slit of the positioning marker 4 formed on the rear lens 2. However, this gap is an allowable error range in positioning.

Further, even if a positional deviation occurs after the initial alignment, accurate alignment can be performed again by using these alignment markers 3 and 4.

Each of the positioning markers 3 and 4 is
For example, a concavo-convex pattern by etching can be used, and a pattern obtained by etching a metal film or the like can also be used. Alternatively, in the case of a molded lens, it is possible to provide a mark on the mold side and transfer the mark to use it as a positioning marker.

Next, a method of aligning the optical axis of the lens and the light transmitting hole in the front lens 1 having the light shielding film 3 will be described.

FIGS. 5 to 1 show the outline of the manufacturing process of the optical element.
As shown in FIG.

The following five 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. (E) forming a light-shielding film and forming a light-transmitting hole therein;

FIG. 5 shows the above step (a). First, a photosensitive material is applied on a substrate 11 made of an optical material by a spin coating method or the like, and a mask material layer 12 is formed.
To form

Next, as shown in FIG. 6, the mask material layer 12 is patterned by exposure and development to form a mask 13 corresponding to each lens.

Then, as shown in FIG. 7, 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 13 into a shape having an optically gentle curved surface.

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 carried out at a temperature of 200 ° C. or more, the phenomenon that any resist material deteriorates (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.

From the experimental results, as a condition for the mask material to be rounded by heat treatment to obtain an optically smooth surface, 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.

Further, 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 reproduced. It is desirable that the glass transition temperature Tg of the mask material be higher than the storage temperature (room temperature) or the processing temperature (around room temperature) because the glass material becomes less easy.

Here, generally, the glass transition point Tg refers to a temperature at which a material is in a glassy state, that is, a temperature at which 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, after the mask 13 is deformed into a round shape, a shape corresponding to the shape of the mask 13 is formed on the optical material as shown in FIG. Specifically, a shape corresponding to the shape of the mask 13 is formed on the optical material using a dry etching method. This is the hemispherical lens 14.

In the present invention, at this time, the hemispherical lens 1
4, the alignment marks 15 are simultaneously formed.

In this example, a fused quartz substrate was used as the glass material of the substrate 11, a photosensitive material was applied to a thickness of about 20 μm, and a circular pattern of about 120 μm was formed by the 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 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 of the manufactured optical lens where the substrate 11 and the mask 13 are in contact does not move even after the heat treatment process, the shape of the mask 13 is defined by the boundary line.

Here, since the boundary of the mask 13 is defined by a photomask used when exposing the photosensitive material, the position of the optical lens is formed at an extremely high precision. Further, the height of the optical lens is determined by the thickness of the mask 13.

In the optical lens manufactured as described above, since it is defined by a 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.

Then, the optical lens is adjusted to a predetermined thickness by a polishing process, and as shown in FIG. 9, light is shielded on the surface of the substrate 11 made of the optical member on the side opposite to the curved surface. The layer 16 (metal film such as Cr) is formed.

Here, it is preferable to apply an AR coat as a stray light prevention treatment to both surfaces of the light shielding layer 16.

Next, a resist layer 17 is formed on the light-shielding layer 16 as shown in FIG. 10, and the resist layer 17 is patterned using a photomask 18 so as to correspond to the light transmission holes, as shown in FIG. Then, the patterned resist layer 17 is left, and the light-shielding layer 16 is removed by an etching process to form a light transmission hole 16a as shown in FIG.

At this time, the position of the light transmitting hole 16a with respect to the optical lens 14 as the light converging means is adjusted, for example, by adjusting the position of the positioning marker 15 formed around the lens 14 with the position on the photomask 18. What is necessary is just to perform by aligning the position with the marker 19. Thereby, the optical axis of the lens 14 and the center of the light transmission hole 16a can be matched with high accuracy.

The optical element of the present invention is manufactured as described above. The optical element can be used for an optical pickup of a recording / reproducing apparatus for recording / reproducing on / from an optical recording medium.

FIG. 13 shows an example of the configuration of an optical pickup incorporating the above optical element.

In this optical pickup, the optical element is incorporated as an objective lens 21.

A linearly polarized light beam emitted from a semiconductor laser as a light source and made parallel by a collimator lens is:
The light passes through a polarizing beam splitter (PBS) 22 and a λ / 4 (quarter wavelength) plate 23 to be in a circularly polarized state.

This circularly polarized light beam is focused on the signal recording surface of the optical disk 24 via the objective lens 21 and the disk substrate 25.

The disk substrate 25 is, for example, a thin substrate having a thickness of about 0.1 mm.

The above-mentioned optical element, that is, the objective lens 21 has an NA of 0.7 to 0.7 which is formed by combining two lenses.
0.95 lens.

The light reflected on the signal recording surface returns to the original optical path, passes through the λ / 4 plate 23, and becomes a linearly polarized light rotated by 90 degrees with respect to the forward linearly polarized light direction.

This light beam is reflected by the polarizing beam splitter 22, passes through a focusing lens (condensing lens) 26 and a multi-lens 27, and passes through a photodetector (PD).
By 28, it is detected as an electric signal.

The multi-lens 27 is a lens whose entrance surface is a cylindrical surface (cylindrical surface) and whose exit surface is a concave surface. The multi-lens 27 imparts astigmatism to the incident light beam to enable detection of a focus error signal by a so-called astigmatism method.

The photodetector 28 is, for example, a six-element photodiode, and outputs an electric signal for performing focus adjustment by the astigmatism method and tracking adjustment by the so-called three-beam method.

[0061]

As is apparent from the above description, according to the present invention, even if there is a molding error in the lens outer shape,
The alignment markers can precisely align the lenses or the optical axis of the lens with the center of the light transmitting hole.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an optical element to which the present invention is applied.

FIG. 2 is a schematic diagram showing a shape of an alignment marker formed on a front lens.

FIG. 3 is a schematic diagram showing the shape of a positioning marker formed on a rear lens.

FIG. 4 is a schematic diagram illustrating a positioning state of a positioning marker.

FIG. 5 is a schematic diagram illustrating a step of forming a mask material layer on a substrate, showing a manufacturing step of the optical element in order of steps.

FIG. 6 is a schematic view showing a mask forming step.

FIG. 7 is a schematic view showing a step of deforming a mask by heat treatment.

FIG. 8 is a schematic view showing a lens forming step by dry etching.

FIG. 9 is a schematic view showing a light shielding layer forming step.

FIG. 10 is a schematic view showing a resist layer forming step.

FIG. 11 is a schematic view showing a step of patterning a resist layer.

FIG. 12 is a schematic view showing a light transmitting hole forming step.

FIG. 13 is a schematic diagram illustrating an example of an optical pickup using an optical element.

[Explanation of symbols]

1 front lens, 2 rear lens, 3, 4 alignment marker

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Claims (8)

[Claims] 1. An optical element having an optical lens formed by dry etching in a part of a light converging means, wherein an alignment marker is formed around the optical lens. 2. The optical element according to claim 1, wherein said light converging means comprises a plurality of lenses arranged on an optical path of light, and is mutually aligned by an alignment marker. 3. A method for manufacturing an optical element, wherein an alignment marker is simultaneously formed around the optical lens when forming an optical lens on one surface of the substrate made of an optical material by dry etching. 4. An optical lens formed on one surface of a substrate made of an optical material by dry etching, and a light-shielding film serving as a light-shielding portion formed on the other surface and patterned by photolithography. 2. The method for manufacturing an optical element according to claim 1, wherein a light transmitting hole for transmitting the light converged by the method is formed. 5. The method for manufacturing an optical element according to claim 4, wherein the adjustment of the position where the light transmitting hole is formed with respect to the optical lens is performed using the alignment marker. 6. 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 that the surface area is reduced, and the mask is formed by dry etching. 4. The method for manufacturing an optical element according to claim 3, wherein an optical lens having a shape corresponding to the shape is transferred and formed on the substrate. 7. The method according to claim 6, wherein the temperature of the heat treatment is higher than the glass transition temperature of the mask material and lower than the carbonization temperature. 8. A recording / reproducing apparatus, wherein the optical element according to claim 1 is used in at least a part of an optical system.