JP2000076695A - Optical head and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve improvement in accuracy and high volume productivity, and miniaturization in an optical head using a solid immersion lens. SOLUTION: This is an optical head provided with an object lens for focusing irradiating light on an optical information medium, and a solid immersion lens which is arranged between the optical information medium and the object lens and converts an effective numerical aperture. In this case, a plate-like object lens substrate 11 which is partly is molded into the object lens 12, and a plate- like solid immersion lens substrate 21 which is partly molded into a solid immersion lens 22 are integrated via a spacer 31, and there exists an air gap between the object lens 12 and the solid immersion lens 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical head capable of recording and reproducing information on an optical recording medium beyond the diffraction limit of light,
It relates to the manufacturing method.

[0002]

2. Description of the Related Art With the increase in capacity and miniaturization of optical recording devices, higher density of recording bits is required.

[0003] The bit size in optical recording corresponds to the spot size diameter of a light beam, and is proportional to the wavelength λ of light and inversely proportional to the numerical aperture NA. For this reason, the direction of higher density is to shorten the wavelength of light and increase the NA of the lens used.
Types.

As a technique for increasing the NA of a lens, a method using a solid immersion lens (SIL: solid immersion lens) has been proposed [US Pat. No. 5,004,307 (Reference 1), Applied Physics Letters]. 57, p2615-
2616 (1990) (Reference 2)].

[0005] SIL is a hemispherical lens made of a transparent material having a large refractive index. The light beam converged by the objective lens is perpendicularly incident on the spherical surface of the SIL and is focused on the center of the bottom surface of the SIL. In this state, when the SIL is brought close to the sample surface and light is incident on the sample at an interval within 1/4 of the wavelength λ, light having a wavelength of λ / n propagates to the sample and a beam spot determined by the diffraction limit The diameter can be reduced to 1 / n.

[0006] Applied Physics Letters 65, p388-390
(1994) (Reference 3) discloses a method in which incident light is refracted by a spherical surface of an SIL and the spot diameter is set to 1 / n ² .
The SIL in this case is not a hemispherical lens, and the thickness is r (1 + 1) when the lens radius is r and the lens refractive index is n.
/ N), that is, a so-called super hemispherical lens.

US Pat. No. 5,497,359 (Reference 4) discloses a SIL, a slider for attaching the SIL, a suspension for supporting the slider, a light source, a disk having a recording medium, and a motor for rotating the disk. An optical recording system is disclosed. As described above, the distance between the SIL and the surface of the sample (in this case, the surface of the recording medium) must be maintained within １ ／ of the wavelength λ of the light. The interval is controlled. The flying slider is used for a magnetic disk drive head in the field of magnetic recording, and the above-mentioned distance (flying amount) is used.
Is a technology that can stably be controlled to 100 nm or less.

[0008] Applied Physics Letters 68, P141-143 (19
96) (Document 5) reports an example in which a slider to which the above-described SIL is attached is incorporated in an optical pickup head, and recording and reproduction are performed using a magneto-optical recording medium using TeFeCo as a recording material. In this example, the SIL is made of glass with a refractive index of 1.83 and has a flying height of 3 nm at 150 nm.
A spot diameter of 60 nm is realized.

[0009]

As shown in References 1 and 2, a microscope using SIL observes a line-space of 100 nm, and the resolution is greatly improved. However, in order to perform high-speed recording and reproduction on an optical recording medium, it is necessary to integrate the SIL with the flying slider as shown in References 4 and 5. However, in Literatures 4 and 5, since the method of bonding the SIL to the slider is adopted, it takes a great deal of time to manufacture and is not suitable for mass production.

In an optical head utilizing SIL, S
An objective lens for focusing on the IL is required, and this objective lens needs to be positioned with extremely high precision with respect to the SIL. However, Document 4 only describes an example in which a support is mounted on a slider, and the support is mounted with an objective lens together with an assembly including a semiconductor laser and a photodetector. With such a structure, there are problems that it is difficult to perform high-precision positioning, mass production is difficult, and the optical head is enlarged. On the other hand, Literature 5 incorporates a slider on which an SIL is mounted in a normal magneto-optical disk test system, and does not consider integration of an objective lens and a slider and downsizing.

The present invention has been made under such circumstances. An object of the present invention is to realize an improvement in accuracy, an improvement in mass productivity, and a reduction in size in an optical head using a solid immersion lens.

[0012]

The above object is achieved by the following (1).
This is achieved by any one of the above configurations (6) to (6). (1) An optical head including an objective lens for condensing irradiation light onto an optical information medium, and a solid immersion lens provided between the optical information medium and the objective lens and converting an effective numerical aperture. There is a plate-shaped objective lens substrate that is partially molded to be an objective lens, and a plate-shaped solid immersion lens substrate that is partially molded to be a solid immersion lens, via a spacer. An optical head that is integrated and has a gap between the objective lens and the solid immersion lens. (2) The optical head according to (1), wherein the objective lens substrate and the solid immersion lens substrate are made of glass, and the spacer is made of silicon. (3) The optical head according to (1), wherein the objective lens substrate and the solid immersion lens substrate are made of silicon, and the spacer is made of glass. (4) The optical head according to any one of (1) to (3), wherein the objective lens substrate, the solid immersion lens substrate, and the spacer constitute at least a part of the slider. (5) A method for manufacturing an optical head according to any one of the above (1) to (4), wherein an objective lens array substrate on which a plurality of objective lenses are formed, and a solid immersion lens array substrate on which a plurality of solid immersion lenses are formed. To
A method for manufacturing an optical head, comprising a step of cutting out a plurality of optical heads after integrating them with a spacer therebetween. (6) The method of manufacturing an optical head according to (5), wherein the objective lens array substrate and the solid immersion lens array substrate are integrated with the spacer by an anodic bonding method.

[0013]

FIG. 1 shows a main part of an example of the configuration of an optical head according to the present invention. The optical head includes an objective lens 12 for condensing irradiation light on an optical recording medium and a solid immersion lens (hereinafter, SI) for converting an effective numerical aperture.
L) 22. The objective lens 12 is formed by molding a part of a plate-shaped objective lens substrate (hereinafter, an OL substrate) 11, and the SIL 22 is formed by molding a part of a plate-shaped SIL substrate 21. ing. O
The L substrate 11 and the SIL substrate 21 are formed by a plate-like spacer 31.
Are integrated through Spacer 31 has through hole 3
2 is provided, and between the objective lens 12 and the SIL 22
There is a gap due to the through hole 32.

The objective lens 12 is made of the same material as the OL substrate 11, and the SIL 22 is made of the same material as the SIL substrate 21. The OL substrate 11 and the SIL substrate 21 may be made of the same material or different materials. A constituent material of each substrate may be appropriately selected from materials that function as lenses at the wavelength of light to be used. The thickness of the flat portion of each of the OL substrate 11 and the SIL substrate 21 is based on the lens design.
What is necessary is just to determine suitably considering each material and the wavelength of the light to be used, but in general, the thickness of the OL substrate is 200 μm
The thickness of the SIL substrate is from 200 μm to 1 m
What is necessary is just to select from the range of m.

The spacer 31 is not limited to the illustrated example, and may have any structure as long as the distance between the two substrates can be accurately maintained and a manufacturing method described later can be applied. For example, the spacer 31 may be in a mesh shape. The thickness of the spacer 31, ie, OL
The distance between the substrate 11 and the SIL substrate 21 is
May be appropriately determined based on the beam diameter of the parallel ray incident on the SIL 22 and the numerical aperture of the objective lens 12 so that the bottom of the SIL 22 is focused, but may be generally selected from the range of 1 to 3 mm.

As a preferred combination of both substrates and spacers, a combination of both substrates made of glass and a spacer made of Si, and a combination of both substrates made of Si
And the spacer is made of glass. Glass and Si can be integrated with high precision and easily by the anodic bonding method as described later. When both substrates are made of glass, it is not necessary that both substrates have the same composition, and an optimal composition may be selected according to the optical properties required for each. In addition, at least one of the substrates may be made of resin.

In the illustrated example, the objective lens 12 is a plano-convex lens whose convex surface faces the SIL 22 side. However, the convex surface may face the opposite side, and it may be a biconvex lens or a meniscus lens. Good. The SIL 22 in the illustrated example has a shape in which a hemisphere is placed on a flat plate,
Although it is a so-called super hemisphere, a structure in which the flat portions are combined to form a hemisphere may be used. The radius of curvature of the SIL 22 may be appropriately determined according to the required effective aperture ratio.

Next, a method for manufacturing the optical head of the present invention will be described.

In this method, as shown in FIG. 2, an objective lens array substrate (hereinafter, referred to as an objective lens array substrate) on which a plurality of objective lenses 12 are formed.
An OL array substrate) 10 and a solid immersion lens array substrate (hereinafter, SIL array substrate) 20 on which a plurality of SILs 22 are formed are integrated with a spacer substrate 30 interposed therebetween. And by cutting out the integrated substrate,
Obtain multiple optical heads simultaneously.

First, the case where the OL array substrate 10 and the SIL array substrate 20 are made of glass and the spacer substrate 30 is made of Si will be described.

The OL array substrate 10 and the SIL array substrate 20 can be manufactured by cutting a glass. Further, for example, it can be formed by a glass thermal deformation method as described in JP-B-61-46408.

The formation of the through holes 32 in the spacer substrate 30 can be performed by etching with an alkaline solution. An example of the process in that case will be described with reference to FIG. First, a silicon nitride film 42 is formed on the surface of a Si (100) substrate 41, and a photoresist 43 is applied thereon, and the photoresist 43 is patterned to form a silicon nitride film 42.
A hole reaching 1 is formed (1). The silicon nitride film 42 is formed by, for example, LPCVD (Low Pressure Chemical Vapor Depo) using SiH ₄ and NH ₃ as source gases.
sition) may be used, but other methods may be used. For etching the silicon nitride film 42, RIE (Reac
tive ion etching) or a wet etching method using an aqueous solution of hydrogen fluoride. Next, the Si (100) substrate 41 is etched using the silicon nitride film 42 as an etching mask to form the through holes 32 (2). For this etching, KOH
An aqueous solution can be used. As is well known, since the etching rate of Si is extremely different between the (100) plane and the (111) plane, this etching is anisotropic etching. Therefore, the through hole 32 has a quadrangular pyramid shape whose inner side surface is the (111) plane. For this reason, at the time of assembly, it is easy to make the optical axes of the large-diameter objective lens and the small-diameter SIL coincide. Finally, the silicon nitride film 4
2 is removed (3).

Integration of OL array substrate 10 and spacer substrate 30 and SIL array substrate 20 and spacer substrate 3
It is preferable to use the anodic bonding method for integration with zero. The anodic bonding method is a method in which an alkali glass and Si are brought into close contact with each other and an electric field is applied so that the two can be uniformly bonded, and is a well-known method in the silicon micromachining technology. If the center of the objective lens 12 and the center of the SIL 22 are accurately aligned and joined by an anodic bonding method, the objective lens 12 and the SIL 22
Deviation of the optical axis between them and the variation in the distance between them can be avoided. Further, the objective lens 12 and the SIL 22
Is determined by the spacer substrate 30 made of Si. In the present invention, it is easy to control the thickness of the spacer substrate 30 with high accuracy. Therefore, in the present invention, it is easy to accurately position the focal point on the bottom surface of the SIL 22. The conditions in the anodic bonding method are not particularly limited, but usually, the voltage applied between the glass substrate and the Si substrate is preferably about 300 to 500 V, and the bonding temperature is preferably about 300 to 400 ° C. .

OL array substrate 10 and SIL array substrate 2
FIG. 4 is a cross-sectional view showing a state in which 0 and 0 are integrated via a spacer substrate 30. In this integrated state, cutting is performed at a location indicated by a broken line in the drawing to cut out the device. The cut-out element may be used as a slider, or the cut-out element may be used by bonding it to a separate slider. In any case, the coincidence of the optical axes of the objective lens and the SIL and the distance between them are maintained without deviation.

When the cut element itself is used as a slider, for example, as shown in FIG.
1 is processed so that the shape of the bottom surface functions as a slider. In the illustrated example, a tapered portion 23 and a rail 24 are formed on the lower surface of the SIL substrate 21 similarly to the slider of the floating head in the magnetic disk device. Also, since the slider is lowered on the side opposite to the tapered portion 23 when flying, the S
A chamfer 25 is provided on the left end side of the IL substrate 21 in FIG.
The configuration is such that the access of the IL 22 to the optical information medium is not hindered. Further, in order to make the bottom surface of the SIL 22 close to the optical information medium, the vicinity of the bottom surface of the SIL 22 is not etched when forming the rail 24, but is left in a disk shape. SIL
The formation of the tapered portion 23, the rail 24, and the chamfered portion 25 on the lower surface of the substrate 21 and other shape processing can be performed by etching or the like before and / or after cutting out the element. For example, in FIG. 4, the rails 24 are formed on the lower surface of the SIL array substrate 20 before the element is cut out.

The lower surface of the SIL substrate 21 is made of DLC (diamond-like carbon), carbon, or the like, like the slider in the magnetic disk drive, for protection and friction reduction when the optical information medium is brought into contact with or sliding on the optical information medium. A protective film may be provided. These may be formed by a CVD method, a sputtering method, or the like. The protective film is preferably formed to be extremely thin or formed in a region excluding the SIL so as not to hinder the function of the SIL.

In order to prevent fine dust generated by contact or sliding with the optical information medium from adhering to the SIL, a concave portion is provided around the SIL 22 on the lower surface of the SIL substrate 21 so that the dust is trapped before reaching the minute opening. It is also preferable to adopt a configuration in which: The shape of the recess is preferably a donut shape surrounding the SIL. This recess is
Although it can be formed by patterning the lower surface of the SIL substrate 21, it can also be formed by patterning the protective film made of DLC or the like or adjusting the thickness of a part of the protective film.

As described above, by adopting a configuration similar to that of the flying head in the magnetic disk drive, the interval between the SIL and the optical information medium can be controlled to a constant interval in the range of about several tens to hundreds of nanometers. it can. Therefore, S
The distance between the bottom surface of the IL 22 and the optical information medium is determined by the wavelength λ of the incident light.
, And high-speed recording / reproducing with a light spot having a small diameter exceeding the diffraction limit becomes possible. The optical head of the present invention can be used for reproducing information on a read-only optical information medium and recording and reproducing information on an optical recording medium.

Next, the OL array substrate 10 and the SIL array substrate 20 are made of Si, and the spacer substrate 3
The case where 0 is made of glass will be described.

Since Si transmits light having a wavelength in the infrared region, if Si is processed into a lens shape, it functions as a lens for infrared light. Since infrared light has a long wavelength, it is not originally suitable for the purpose of reducing the spot diameter. However, since the refractive index of Si in the infrared region is as large as about 3.5, the spot diameter is sufficiently small even if the wavelength is long. can do.

The OL array substrate 10 and the SIL array substrate 20 made of Si can be manufactured by using etching of the Si substrate. FIG. 5 shows an example of the process in that case. First, a photoresist 43 is applied to a Si (100) substrate 41 and patterned into a disk shape (1). Next, post-baking is performed at about 180 ° C. to soften the photoresist 43 to form a lens (2). Then, when the Si (100) substrate 41 is etched by RIE, the shape of the photoresist 43 is transferred to the Si (100) substrate 41 (3), and finally, the S
The i (100) substrate 41 has a lens shape (4). The selectivity of the etching rate between the photoresist 43 and Si is
By controlling the composition of the etching gas, a Si lens having a desired shape can be obtained.

The formation of the through holes 32 in the spacer substrate 30 made of glass can be performed by etching. FIG. 6 shows an example of the process in that case. First,
A photoresist 43 is provided on the front and back surfaces of the glass substrate 51.
Is applied and patterned, and openings having dimensions corresponding to the objective lens and the SIL are formed on the front surface and the rear surface, respectively (1). Next, the glass substrate 51 is etched from the surface to the middle of the thickness direction (2).
(1) Etching is performed to penetrate from the back surface to form a through hole 32 (3), and finally, the photoresist 43 is removed (4). In FIG. 6, an objective lens having a different diameter and S
To facilitate alignment of the optical axis with the IL, a step is provided in the middle of the through hole 32, and the diameter is changed up and down. However, if there is no problem with the alignment of the optical axis, a step is provided in the middle of the through hole 32. No need.

In order to integrate the OL array substrate 10 and the SIL array substrate 20 via the spacer substrate 30, it is preferable to use the anodic bonding method described above. Subsequent steps include the OL array substrate 10 and the SIL array substrate 2
This is the same as the case where 0 is made of glass and the spacer substrate 30 is made of Si.

When the OL array substrate or the SIL array substrate is made of resin, for example, Japanese Patent Publication No. 5-709
For example, a plastic lens array as described in JP-A-44 can be used.

[0035]

EXAMPLE 1 A slider having the structure shown in FIG. 1, in which the OL substrate 11 and the SIL substrate 21 were made of glass, and the spacer 31 was made of Si was manufactured in the following procedure.

OL array substrate 10 and SI shown in FIG.
The L array substrate 20 is made of an optical glass (BK7, wavelength 650).
It was manufactured by cutting a mold having a refractive index n = 1.52) in nm. In this embodiment, since the refractive index is high, BK7
However, glass other than optical glass, such as Pyrex, may be used. The thickness of the flat portion of the OL array substrate 10 was 250 μm, and the thickness of the flat portion of the SIL array substrate 20 was 250 μm. The SIL 22 has a super hemispherical structure in which a flat plate portion and a hemispherical portion are combined as shown in FIG.
The radius of curvature r was 380 μm. Flat plate thickness 25
0 μm satisfies the relationship of r / n with respect to the SIL radius r and the refractive index n. Therefore, as shown in the above-mentioned reference 5, light focused on a position at a distance of nr from the center of curvature of the SIL is transmitted from the objective lens along the optical axis to the SI.
By making the light incident on L, the actual focus can be adjusted to the bottom surface of the super hemisphere. In this embodiment, since the wavelength of the incident light is 650 nm, λ / 4 is 162.5 nm. By setting the distance between the bottom surface of the SIL and the optical information medium to 162.5 nm or less, the spot diameter of the light can be reduced to 1 / n ² as compared with the case where only the objective lens is used. In this embodiment, since n = 1.52, the spot diameter is reduced to 1 / 2.31. The improvement of the bit array density by reducing the spot diameter is effective in the track length direction and the track width direction.
3 times.

The formation of the through holes 32 in the spacer substrate 30 was performed according to the procedure shown in FIG. LPCVD using SiH ₄ and NH ₃ was used to form the silicon nitride film 42. RIE was used for etching the silicon nitride film 42. The Si (100) substrate 41 was etched with a KOH aqueous solution. The thickness of the spacer substrate 30 was 1 mm.

Integration of OL array substrate 10 and spacer substrate 30 and SIL array substrate 20 and spacer substrate 3
The anodic bonding method was used for the integration with 0. The conditions in the anodic bonding method were 400 V and 350 ° C.

Next, the obtained joined body is etched to form a tapered portion 23, a rail 24 and a chamfered portion 25,
The element was cut out by a dicing saw to obtain a slider. The dimensions of the slider are 2mm in width, 4mm in length, and 1.
It was 5 mm. The rail width was 0.5 mm.

When a suspension was attached to this slider and was floated on a phase-change optical recording disk, λ
It stably floated with a flying height of 100 nm within / 4
A recording mark having a diameter of 80 nm could be formed.

Embodiment 2 The OL substrate 11 and the SIL substrate 21 having the structure shown in FIG. 1 are made of Si (refractive index n = 3.3 at a wavelength of 1.3 μm).
5), and a slider in which the spacer 31 was made of glass was manufactured by the following procedure.

The OL array substrate 10 and the SI shown in FIG.
The L array substrate 20 was manufactured by the method shown in FIG.
The SIL 22 has a super hemispherical structure similar to that of the first embodiment. In this embodiment, the wavelength of the incident light is set to 1.3 times which is twice that of the first embodiment.
μm. Therefore, the reduction of the spot diameter is disadvantageous in terms of wavelength, but in this embodiment, since the refractive index of the SIL 22 is as large as 3.5, 1 / n ² becomes 12.25, and as a result, the spot diameter becomes Wavelength 6 without using SIL
Compared to the case where 50 nm incident light is used, the size is reduced to 1 / 6.1.

The formation of the through holes 32 in the spacer substrate 30 was performed by etching the glass substrate 51 as shown in FIG.

Integration of OL array substrate 10 and spacer substrate 30 and SIL array substrate 20 and spacer substrate 3
The anodic bonding method under the same conditions as in Example 1 was used for integration with 0.

After bonding, a slider was formed in the same manner as in the first embodiment, a suspension was attached, and the slider was floated on a phase change type optical recording disk. As in the first embodiment, the slider was stably at a flying height of λ / 4 or less. Thus, a recording mark having a diameter of 200 nm could be formed.

[0046]

According to the present invention, the objective lens array substrate and the S
The substrate is bonded to an IL array substrate via a spacer, and then divided into element units to obtain an optical head. For this reason, the optical axis of the objective lens and the optical axis of the SIL can be accurately matched, and the state does not change. Also,
The distance between the two lenses can be set with high accuracy, and the state does not change. Further, mass production of the optical head is easy. Further, it is possible to reduce the size of the optical head, particularly in the height direction.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of a configuration example of an optical head according to the present invention.

FIG. 2 is a perspective view showing how an objective lens array substrate and a solid immersion lens array substrate are integrated with a spacer substrate interposed therebetween.

FIG. 3 is a diagram illustrating a method of forming a through hole in a spacer substrate made of Si.

FIG. 4 is a cross-sectional view showing a state where an objective lens array substrate and a solid immersion lens array substrate are integrated via a spacer substrate.

FIG. 5 is a diagram for explaining a method of manufacturing an objective lens array substrate and a solid immersion lens array substrate each made of Si.

FIG. 6 is a diagram illustrating a method of forming a through hole in a spacer substrate made of glass.

FIG. 7 is an explanatory diagram of a solid immersion lens having a super hemispherical structure.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 Objective lens (OL) array substrate 11 Objective lens (OL) substrate 12 Objective lens 20 Solid immersion lens (SIL) array substrate 21 Solid immersion lens (SIL) substrate 22 Solid immersion lens (SIL) 23 Tapered portion 24 Rail 25 Chamfered portion Reference Signs List 30 spacer substrate 31 spacer 32 through hole 41 Si (100) substrate 42 silicon nitride film 43 photoresist 51 glass substrate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Shinoura 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Hidehiko Yamaoka 1-13-1 Nihonbashi, Chuo-ku, Tokyo F-term in DK Corporation (reference) 5D119 AA01 AA11 AA22 JA44 JA50 JB02

Claims (6)

[Claims] 1. An optical system comprising: an objective lens for converging irradiation light onto an optical information medium; and a solid immersion lens provided between the optical information medium and the objective lens and configured to convert an effective numerical aperture. A head, in which a plate-shaped objective lens substrate partially molded to be an objective lens and a plate-shaped solid immersion lens substrate partially molded to be a solid immersion lens, form a spacer. An optical head that is integrated through a gap and has a gap between the objective lens and the solid immersion lens. 2. The optical head according to claim 1, wherein the objective lens substrate and the solid immersion lens substrate are made of glass, and the spacer is made of silicon. 3. The optical head according to claim 1, wherein the objective lens substrate and the solid immersion lens substrate are made of silicon, and the spacer is made of glass. 4. The optical head according to claim 1, wherein the objective lens substrate, the solid immersion lens substrate, and the spacer form at least a part of a slider. 5. The method for manufacturing an optical head according to claim 1, wherein an objective lens array substrate on which a plurality of objective lenses are formed, and a solid immersion lens array substrate on which a plurality of solid immersion lenses are formed. And a method for manufacturing an optical head, comprising cutting out a plurality of optical heads after integrating them with a spacer interposed therebetween. 6. The method for manufacturing an optical head according to claim 5, wherein the integration of the objective lens array substrate and the solid immersion lens array substrate with the spacer is performed by an anodic bonding method.