JP2002350609A - Method for manufacturing optical element, optical element and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive object lens with high NA which can be easily manufactured. SOLUTION: The optical element (Fig. 2 (g)) having lenses formed on both surfaces of a transparent substrate is manufactured in the process (Fig. 2 (b)) of forming a lens form by irradiating a photoresist applied on a transparent substrate with predetermined beams of light (Fig. 2 (a)), a process of transferring the lens form to the transparent substrate by dry etching (Fig. 2 (c)), and repeating the above processes on both surfaces of the upper and lower faces of the transparent substrate (Fig. 2 (d) to Fig. 2 (f)).

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, an optical element, and an optical pickup device.
The present invention relates to a method for manufacturing an optical element used for an optical recording medium, an optical element, and an optical pickup device.

[0002]

2. Description of the Related Art In recent years, higher recording densities of optical discs have been demanded, and as one of the methods, a method using a solid immersion lens or a high NA lens (high numerical aperture lens) has been proposed.

In a conventional optical pickup device, by using a two-group objective lens configuration including two lenses, it is possible to increase the NA (numerical aperture) of the objective lens and reduce the spot diameter of laser light. Had become. By using such a lens, it is possible to increase the recording density of the optical disc.

[0004] For example, Japanese Patent Application Laid-Open No. 2000-11388, "Optical information recording / reproducing apparatus and optical information recording / reproducing method",
Japanese Patent Application Laid-Open No. 11-144293, entitled "Optical Head and Optical Recording Apparatus", and Japanese Patent Application Laid-Open No. The objective lens is constituted by one lens, and thereby the NA of the objective lens is increased, thereby making it possible to increase the recording density of the optical disc.

FIGS. 11, 12 and 13 are diagrams showing the configuration of a conventional two-lens objective lens and its peripheral portion disclosed in the above-mentioned publication. In the figure, reference numerals 101, 111 and 121 are first lenses,
Reference numerals 102, 112 and 122 denote second lenses. Reference numerals 103 and 113 are optical disks, 104 and 105 are actuators, and 114 and 124 are sliders.

In the objective lens shown in FIG. 11, an independent first lens 101 and second lens 102 constitute an objective lens to realize a high NA. The objective lens shown in FIG. 12 has a configuration in which a first lens 111 and a second lens 112 are mounted on a slider 114. Further, the objective lens shown in FIG. 13 has a configuration in which the first lens 121 and the second lens are formed in the slider 124. Both the objective lens shown in FIG. 12 and the objective lens shown in FIG. 13 realize a high NA, and can be arranged very close to the optical disk by floating on an optical disk rotating at high speed. I have.

[0007]

However, the prior art has the following problems. JP-A-2000-113
In a configuration in which two lenses are driven by actuators, respectively, as in the technique disclosed in JP-A-88-88, there is a problem that it is extremely difficult to ensure the positional accuracy of the two lenses.

[0008] Also, with the aim of increasing the density, the optical disk 103
If the side lens 102 (see FIG. 11) is a solid immersion lens, the lens 102 must be located very close to the optical disk 103 (less than the wavelength of the light source). A configuration such as mounting is used. However, JP 20
In the configuration of 00-11388, there is also a problem that the actuator 105 is heavy due to the presence of the actuator 105 and is difficult to mount on the slider.

In the technique disclosed in Japanese Patent Application Laid-Open No. 11-144293, a slider is provided with a solid immersion lens and an objective lens to reduce the weight. However, there is a problem that it is difficult to perform positioning of the lenses with high accuracy, and since the lenses are assembled one by one, mass productivity is very poor, leading to an increase in cost.

In the technique disclosed in Japanese Patent Application Laid-Open No. H11-045455, two lenses are formed on the same substrate, and the alignment between the lenses is performed with high accuracy. Therefore, a plurality of lenses can be manufactured at the same time. However, in the process of forming the lens shape with the photoresist, the deformation of the photoresist by heat, the deformation of the photoresist by pressure, or the exposure method using a diffusion mask is used, and it is difficult to form a complicated shape such as an aspherical shape. There was a problem.

In general, a factor that determines the size of a spot formed on an optical disk is lens aberration.
In order to suppress aberration with a high NA lens, it is necessary to accurately form a lens shape designed with an aspherical shape.

The present invention has been made in view of the above, and has as its object to provide an easy-to-manufacture and inexpensive high NA objective lens.

[0013]

According to a first aspect of the present invention, there is provided a method for manufacturing an optical element, comprising: irradiating a photoresist coated on a transparent substrate with predetermined light; By performing the step of forming the shape and the step of transferring the lens shape to the transparent substrate by dry etching on both the upper surface and the lower surface of the transparent substrate, lenses are formed on both surfaces of the transparent substrate. Characterized in that an optical element is manufactured.

According to a second aspect of the present invention, there is provided the optical element manufacturing method according to the first aspect, wherein the transparent substrate is coated with a negative photoresist and the negative photoresist is coated. The negative type photoresist is exposed to irradiation light having a predetermined light amount distribution from the opposite side to form a lens.

According to a third aspect of the present invention, in the method of manufacturing an optical element according to the first or second aspect, a concave lens shape is formed on both surfaces of the transparent substrate, and the concave lens shape portion is formed. Is filled with a material having a refractive index different from that of the transparent substrate to form a lens.

According to a fourth aspect of the present invention, in the method of manufacturing an optical element according to the first, second or third aspect, the predetermined light is formed by forming a plurality of lens shapes on the transparent substrate. It is characterized by having been irradiated as follows.

According to a fifth aspect of the present invention, an optical element is manufactured by the optical element manufacturing method according to any one of the first to fourth aspects.

An optical element according to a sixth aspect is the optical element according to the fifth aspect, wherein the transparent substrate is a slider.

An optical element according to a seventh aspect is characterized in that, in the optical element according to the fifth or sixth aspect, an optical element separately manufactured is attached.

The optical element according to claim 8 is the optical element according to claim 7, wherein the attached optical element is a micro prism.

An optical element according to a ninth aspect is the optical element according to the seventh aspect, wherein the attached optical element is a quarter-wave plate.

The optical element according to claim 10 is the optical element according to any one of claims 5 to 9,
A thin-film coil is formed on a surface of the transparent substrate.

According to an eleventh aspect of the present invention, in the optical pickup device, the optical element according to any one of the fifth to tenth aspects is applied to an optical pickup device. The distance from the recording layer of the recording medium is set to １ ／ or less of the wavelength of the light source.

That is, in the present invention, first, a (negative type) photoresist is applied to one surface of a substrate, and is exposed from the back side of the substrate with irradiation light having an appropriate exposure distribution to form a resist pattern. Then, the resist pattern is transferred to the substrate by dry etching. Next, a resist pattern is formed on the opposite surface, and the resist pattern is transferred by dry etching.

In other words, according to the present invention, it is possible to easily and easily manufacture an objective lens composed of two lenses, to perform the alignment with high accuracy, and to easily increase the NA. Can be performed.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) First, an optical element of the present invention will be described. FIG. 1 is a cross-sectional view of an optical element according to the present embodiment.
FIG. 2 is an explanatory view showing an example of a manufacturing process of the optical element in the present embodiment. In the drawing, 1 is a first lens, 2
Is a second lens, 3 is a quartz glass substrate, 4 is a negative photoresist, 5 is a positive photoresist, and 6 is a high refractive material.

The fabrication process will be described. First, a negative photoresist 4 is applied to one surface of a quartz glass substrate 3 and prebaked. Next, light is irradiated from the side on which the negative photoresist 4 is not applied by an exposure method that causes a distribution in the exposure amount, and the quartz glass substrate 3 is irradiated with light.
And exposes the negative photoresist 4 (see FIG. 2).
(See (a)).

Since the amount of resist remaining after development can be controlled by the amount of exposure, exposure is performed so that an exposure amount distribution corresponding to the shape of the first lens 1 is generated, and development is performed on the quartz glass substrate 3. A resist pattern is formed in the shape of the first lens 1 (see FIG. 2B). In addition, as an exposure method that causes a distribution in the exposure amount,
A method using a photomask with optical density distribution,
There is a method of intentionally defocusing at the time of exposure using a mask having a distribution of the density of the fine dot pattern.

Next, the quartz glass substrate 3 on which the resist pattern of the first lens shape 1 was formed was dry-etched to transfer the photoresist pattern onto the quartz glass substrate 3 (see FIG. 2C). In this embodiment, an ECR etching device was used as an etching device for performing dry etching. Etching gas used CF _4,
H ₂ and O ₂ were added to this to adjust the etching rate and etching selectivity (quartz glass etching rate / photoresist etching rate).

When the selectivity is set to about 1, the photoresist pattern is transferred onto the quartz glass wafer in almost the same shape and size. When the selection ratio is larger than 1, the transfer is enlarged and transferred in the height direction of the photoresist pattern shape, and when the selection ratio is smaller than 1, the transfer is reduced and transferred in the height direction of the photoresist pattern shape.

Next, a positive photoresist 5 is formed on the surface of the quartz glass substrate 3 opposite to the surface on which the first lens 1 is formed.
Was applied and exposed (see FIG. 2D). continue,
Exposure was performed from the side on which the positive photoresist 5 was applied (see FIG. 2E). Exposure was performed in the same manner as described above so as to produce an exposure distribution, and a concave resist pattern was formed.

After forming the concave resist pattern, dry etching is similarly performed to transfer the concave type to the quartz glass substrate 3 (see FIG. 2F), and the high refractive material 6 is embedded to form the second lens 2. (See FIG. 2 (g)).

In general, negative photoresists can be relatively thick, and are often excellent in heat resistance.
In the lens forming step (FIG. 2A to FIG. 2C), a lens having a relatively high height is formed. In this embodiment, a lens pattern having a height of about 100 μm was formed using THB-430N manufactured by JSR Corporation.

On the other hand, if the thickness of the positive resist is too large, cracks in the resist pattern occur due to heat during dry etching, so that the thickness of the positive resist cannot be too large. However, the thickness is sufficient to form the second lens 2 in the optical element of the present embodiment shown in FIG.

As described above, by manufacturing the optical element by the manufacturing method described in this embodiment, the first lens 1 having a larger diameter and a smaller radius of curvature than the conventional one can be manufactured. In other words, according to the manufacturing method described in the present embodiment, a lens having a large NA can be manufactured. Since a lens with a large NA can reduce the beam spot size, by using the optical element of this embodiment as an objective lens of an optical pickup device,
Large-capacity recording becomes possible by increasing the recording density.

Further, since the second lens is a solid immersion lens and the distance between the second lens and the recording layer of the optical disk is reduced to １ ／ or less of the wavelength of the light source, it is possible to use near-field light. Further, the spot size can be reduced, and higher recording density can be achieved.

In this embodiment, a quartz glass substrate is used as a substrate for forming a lens. The manufactured lens is transparent to the used light source wavelength of the applied device, and
Other materials may be used as long as they are transparent to the wavelength of the light source of the exposure apparatus that performs exposure in the photolithography process. Needless to say, dry etching conditions need to be changed according to the material, including the type of etching gas.

In this embodiment, an ECR etching apparatus is used as a dry etching apparatus. However, an etching apparatus using another method such as an ICP etching apparatus may be used.
As a matter of course, if the method or the apparatus is different, the etching rate and the selectivity are different, so that it is necessary to change the etching conditions.

It is to be noted that an optical element in which another lens is attached to the optical element shown in FIG. 1 can also be used. FIG. 3 is a cross-sectional view of an optical element in which a third lens 10 using another quartz glass substrate is attached to the optical element of FIG. Although a detailed description of the optical system is omitted, a lens having a higher NA can be realized by adopting the configuration as illustrated.

The third lens 10 is also the first lens 1
It can be manufactured in the same process as described above. Regarding the bonding, an alignment mark is also formed when a lens shape is formed for each quartz glass substrate 3, and alignment is performed using the alignment mark. In addition, the portions that abut each other can be formed with high precision in the lens forming process, so that the lens spacing can be bonded with high precision. For bonding,
Although an ultraviolet curable resin is used, another adhesive may be used. In addition, it is a matter of course that the bonding can be performed one by one, but a plurality of lenses may be collectively bonded in a wafer process to enhance productivity including cost.

(Embodiment 2) A second embodiment of the present invention will be described. FIG. 4 is a sectional view of the optical element of the present invention,
FIG. 5 is a diagram showing a manufacturing process. 11 is a first lens, and 12 is a second lens.

The manufacturing process will be described. First, similarly to the first embodiment, a negative photoresist 4 is applied to one surface of the quartz glass substrate 3 and prebaked. Next, light is irradiated from the side on which the negative photoresist 4 is not applied and is transmitted through the quartz glass substrate 3 to expose the negative photoresist 4 by an exposure method that causes a distribution in the exposure amount (FIG. 5 (a)).

At this time, a resist pattern is formed on the quartz glass substrate 3 by exposing and developing so that an exposure amount distribution corresponding to the concave shape is generated unlike the shape shown in the first embodiment. (See FIG. 5B). An exposure method that produces a distribution in the amount of exposure can be performed by the method described in the first embodiment. The quartz glass substrate 3 on which the concave resist pattern is formed is dry-etched as in the first embodiment, and the photoresist pattern is transferred to the quartz glass substrate 3 (FIG. 5C).

The second lens shape is formed in the same manner as in the first embodiment (see FIGS. 5 (d) to 5 (f)). Finally, an optical component having the structure shown in FIG. 4 is manufactured by embedding the high refractive material 6 in each of the concave portions of the first lens and the second lens (see FIG. 5G). Note that, like the first embodiment, a first photoresist formed using a negative photoresist is used.
In the lens process (1), a lens having a relatively high height is formed.

As described above, by manufacturing an optical element by the manufacturing method described in this embodiment, a first lens having a larger diameter and a smaller radius of curvature can be manufactured. That is, a lens having a large NA can be manufactured by the manufacturing method of the second embodiment.

Looking at the structure of the optical element of this embodiment, it can be seen that the optical element can have a parallel plate structure. Therefore, it is possible to easily mount another optical element on the optical element. FIGS. 6 and 7 are explanatory views showing an example in which another optical element is mounted on the optical element of the second embodiment. Here, 7 is an optical disk, 8 is a micro prism, and 9 is a 1/4 wavelength plate.

FIG. 6 shows the optical element of the second embodiment with the microprism 8 mounted thereon as described above. By mounting the microprism 8, the optical path can be deflected by 90 °. If such a composite optical element is used for an optical pickup device, the device can be made thinner.

FIG. 7 shows the optical element of the second embodiment, on which the quarter-wave plate 9 is mounted and integrated, as described above.
The quarter-wave plate 9 has a characteristic that when the direction of the optical axis of the crystal is set to 45 ° with respect to the plane of polarization of the linearly polarized incident light, the linearly polarized incident light is converted into circularly polarized light. In addition, when circularly polarized light is incident, the light is converted into linearly polarized light.

As shown in FIG. 7, the linearly polarized incident light is converted into circularly polarized light by the quarter-wave plate 9 and reflected by the optical disk 7. When the reflected light passes through the quarter-wave plate 9, the linearly polarized light is again emitted. At this time, the plane of polarization can be changed by 90 ° between the incident light and the reflected light. Utilizing this, in a general optical pickup, the optical path is deflected by using a quarter-wave plate, a polarization beam splitter, a polarization hologram, and the like. As shown in FIG.
By using an optical element on which the four-wavelength plate 9 is mounted and integrated into an optical pickup device, it is possible to reduce the size and weight of the device. Note that a configuration in which both the microprism 8 and the 波長 wavelength plate 9 are mounted may be adopted.

(Embodiment 3) A third embodiment of the present invention will be described. FIG. 8 is a sectional view of an optical element according to the third embodiment. The shape of the slider is also formed on the quartz glass substrate 14. The step of forming the shape of the slider on the quartz glass substrate 14 can be performed simultaneously with the step of forming the concave shape of the second lens (the portion filled with the high refractive index material 12), so a new step is added. No need to
The increase in cost can be suppressed.

As described in the first embodiment, the optical pickup using the near-field light using the second lens as a solid immersion lens can make the spot size extremely small. It is very effective. However, the second lens must be brought very close to the recording layer of the optical disc (not shown).

Here, the slider applies the principle of the air bearing, and can be floated very close to the surface of the disk rotating at high speed. Therefore, by mounting the solid immersion lens on the slider, it is possible to dispose the optical pickup very close to the optical disk. Further, if the structure described in this embodiment is adopted, an objective lens for an optical pickup in which a lens and a slider are integrated can be easily manufactured, so that a large-capacity optical pickup device can be manufactured at low cost. Becomes

(Embodiment 4) A fourth embodiment of the present invention will be described. FIG. 9 is a sectional view of an optical component according to a fourth embodiment. Two lens groups each including a first lens 1 and a second lens 2 are formed on the same quartz glass substrate 3. Since the optical element having the structure shown in the drawing can be manufactured by exactly the same method as the manufacturing method described in the first embodiment,
Here, the description is omitted.

In the fourth embodiment, by employing a configuration having two pickup optical systems, it is possible to form two spots on the optical disc, and it is possible to record / record at two locations simultaneously.
Reproduction can be performed. This means that the recording and reproducing speed can be improved. Note that recording may be performed at two locations or playback may be performed at both locations, but playback may be performed on one side and recording may be performed on the other.

Although FIG. 9 shows a state in which two lens groups are formed, the number of lens groups is not limited to two and may be more. Further, as described in the third embodiment, since the slider shape can be formed on the quartz glass substrate 3 shown in FIG. 9, it is easy to form a plurality of lens groups on the same slider. Can be made.

(Embodiment 5) A fifth embodiment of the present invention will be described. FIG. 10 is a sectional view of an optical element according to a fifth embodiment. In the figure, reference numeral 15 denotes a thin-film magnetic coil. The thin film magnetic coil 15 is formed on the quartz glass substrate 3 on which the first lens is formed by a thin film forming process such as sputtering or vapor deposition, a photolithography process, and an etching process. These processes can also be performed by a wafer process. With such an optical element structure, the optical element shown in FIG. 10 can be used as an objective lens for magneto-optical recording.

[0057]

As described above, according to the present invention,
First, a (negative-type) photoresist is applied to one surface of a substrate, and a resist pattern is formed by exposing from the back side of the substrate, and the resist pattern is transferred to the substrate by dry etching. Next, a resist pattern is formed on the opposite surface, and the resist pattern is transferred by dry etching. Through these steps, it is possible to provide an easy-to-manufacture and inexpensive high-NA objective lens (optical element).

Further, since the optical element is manufactured by a wafer process, an optical element can be manufactured at low cost. Furthermore, by configuring an optical pickup device using the optical element of the present invention, it is possible to realize an optical pickup device that can read and write a very large-capacity recording medium.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical element according to a first embodiment.

FIG. 2 is a diagram illustrating a manufacturing process of an optical element in Example 1.

FIG. 3 is a cross-sectional view of the composite optical element according to the first embodiment.

FIG. 4 is a sectional view of an optical element according to a second embodiment.

FIG. 5 is a view for explaining a manufacturing process of an optical element in Example 2.

FIG. 6 is a cross-sectional view of a composite optical element according to a second embodiment.

FIG. 7 is a sectional view of a composite optical element according to a second embodiment.

FIG. 8 is a sectional view of an optical element according to a third embodiment.

FIG. 9 is a sectional view of an optical element according to a fourth embodiment.

FIG. 10 is a sectional view of an optical element according to a fifth embodiment.

FIG. 11 is a configuration diagram of a conventional objective lens including two lenses.

FIG. 12 is a configuration diagram of a conventional objective lens including two lenses.

FIG. 13 is a configuration diagram of a conventional objective lens composed of two lenses.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 1st lens 2, 12 2nd lens 3 Quartz glass substrate 4 Negative photoresist 5 Positive photoresist 6 High refraction material 7 Optical disk 8 Microprism 9 1/4 wavelength plate 10 Third lens 14 Slider Shaped glass substrate 15 Thin film magnetic coil

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B29K 101: 10 B29K 101: 10

Claims (11)

[Claims] A step of irradiating a photoresist applied on a transparent substrate with predetermined light to form a lens shape; and a step of transferring the lens shape to the transparent substrate by dry etching. An optical element manufacturing method, wherein an optical element having lenses formed on both surfaces of the transparent substrate is manufactured by performing the process on both upper and lower surfaces of the transparent substrate. 2. A method in which a negative photoresist is applied to the transparent substrate, and the negative photoresist is exposed to light having a predetermined light amount distribution from a surface opposite to a surface on which the negative photoresist is applied. The method for producing an optical element according to claim 1, wherein a lens is formed. 3. A concave lens shape is formed on both surfaces of the transparent substrate, and a lens having a refractive index different from that of the transparent substrate is filled in the concave lens shape portion to form a lens. The method for producing an optical element according to claim 1. 4. The method of manufacturing an optical element according to claim 1, wherein the predetermined light is applied so as to form a plurality of lens shapes on the transparent substrate. 5. An optical element produced by the method for producing an optical element according to claim 1. Description: 6. The optical element according to claim 5, wherein the transparent substrate is a slider. 7. The optical element according to claim 5, wherein an optical element manufactured separately is attached. 8. The optical element according to claim 7, wherein the attached optical element is a micro prism. 9. The optical element according to claim 7, wherein the attached optical element is a quarter-wave plate. 10. The optical element according to claim 5, wherein a thin-film coil is formed on a surface of the transparent substrate. 11. An optical element according to claim 5, wherein the distance between a pickup-side surface of the optical element and a recording layer of an information recording medium is determined by a light source wavelength. An optical pickup device characterized in that the distance is 1/4 or less.