KR20000046141A - Optical head of proximate field and production method thereof - Google Patents

Abstract

PURPOSE: An optical head of proximate field and its production method are provided to increase a generating efficiency of proximate field with the optical head of new structure. CONSTITUTION: A substrate(11) is prepared. An etching stop layer differed an etching property to the substrate is formed in a lower face of the substrate. A first aperture having a wide upper face and a narrow lower face is formed by etching an upper face of the substrate to expose the etching stop layer. A reflecting film(13) is formed in a front face of the substrate contained the first aperture. The etching stop layer is removed. A smaller second aperture than the first aperture is formed by punching a hole in a regular area of the reflecting film. Thereby, an optical head of proximate field is produced.

Description

Near-field optical head and its manufacturing method

The present invention relates to a near field optical head for a high density optical disc in a read only or rewritable optical disc and a method of manufacturing the same.

Starting from CD-ROM, optical disc technology has been continuously developed.

As a result, a DVD-ROM with a capacity of 4.7 GB is commercialized for playback only, a 2.6 GB recording capacity is commercialized for a rewritable DVD-RAM, and a next-generation version, which will have a recording capacity of 4.7 GB, will be commercialized soon. Seems to be.

Currently, the trend being studied is also focused on increasing the recording density.

However, due to the diffraction limit, the size of the laser beam spot used cannot be reduced below the wavelength length, and the density is slowed down.

Therefore, researches for discovering a short wavelength laser light source are in progress, and a blue band laser is currently being developed.

One of the methods for such high density is a method using near field optics.

If the optical fiber, which acts as a laser waveguide, is reduced to sub-wavelength, or the aperture from which the laser is emitted is reduced to sub-wavelength, the distance of proximity (less than tens of nanometers) The theory of near-field optics is that in Esau, light can be created to maintain a very small size laser spot.

However, near field optics have two problems.

One is that the near field is only maintained within a very small area, a few tens of nm from the fiber tip or aperture tip.

Therefore, a difficulty arises in that the distance between the optical head and the recording medium must be kept constant in a very narrow area.

The other is that the light efficiency of near field is very low.

That is, compared with the laser power used, the power of the light representing the near field is very small and the efficiency is extremely low.

That is why most of the energy is absorbed by the fiber tip or aperture tip and converted into heat.

The structure of the head for the near field optics using the conventional aperture is shown in FIGS. 1A and 1B.

1A is a plan view showing a conventional near field optical head, and FIG. 1B is a sectional view.

As shown in FIGS. 1A and 1B, conventionally, an aperture (about 100 nm) hole smaller than a laser wavelength was formed by chemical etching on a silicon substrate.

The main problem with this structure is that the near field generation efficiency is very low.

That is, the power of the near field is very small compared to the power of the propagating wave input.

The power of the near field is known to decrease exponentially with distance from the aperture.

In this case, most of the laser energy applied before the near field oscillates at the end of the aperture having a size of 100 nm or less is scattered in the reflecting film and is mostly lost as thermal energy.

The present invention has been made to solve such problems, and an object thereof is to provide a near field optical head and a method of manufacturing the same, which can increase the near field generation efficiency using a new optical head.

1A and 1B are a plan view and a cross-sectional view showing a conventional near field optical head

2 is a structural cross-sectional view showing a near field optical head according to the first embodiment of the present invention.

3A to 3F are cross-sectional views showing a manufacturing process of a near-field optical head according to the first embodiment of the present invention.

4 is a structural cross-sectional view showing a near field optical head according to a second embodiment of the present invention.

5A to 5G are cross-sectional views showing a manufacturing process of a near field optical head according to a second embodiment of the present invention.

Explanation of symbols for main parts of the drawings

11,21 substrate 12,22 photoresist

13,23: reflective film 24: tertiary nonlinear film

A feature of the near-field optical head according to the present invention is a substrate having a first aperture, a reflective film formed on the front surface of the substrate including the first aperture, and formed in a predetermined region of the first aperture and being relatively more than the first aperture. It consists of a small second aperture.

Another feature of the present invention is that the first aperture is formed with a wide top and a narrow bottom.

Another feature of the invention is that a tertiary nonlinear film is formed on the first reflecting film.

Features of the method of manufacturing a near-field optical head according to the present invention include preparing a substrate, forming an etching stop layer having different etching properties from the substrate on the lower surface of the substrate, and etching the upper surface of the substrate to expose the etching stop layer. Forming a first aperture having a wide top surface and a narrow bottom surface, forming a reflective film on the entire surface of the substrate including the first aperture, removing an etch stop layer, and a reflective film formed in the first aperture region. Forming a second aperture having a smaller size than the first aperture by drilling a hole in a predetermined region of the second aperture.

Another feature of the invention is that after forming the reflective film, further comprising forming a tertiary nonlinear film thereon.

The near field optical head and the method of manufacturing the same according to the present invention having the above characteristics will be described with reference to the accompanying drawings as follows.

First embodiment

FIG. 2 is a structural cross-sectional view showing a near-field optical head according to a first embodiment of the present invention. As shown in FIG. 2, first, a relatively large hole having a size of about 1 to 2 μm is formed in a silicon substrate, and then a metal deposited thereon. A small hole below the laser wavelength is drilled in the reflective film at about 60 nm and used as an aperture.

In this case, the light reflected along the inclined surface of the silicon substrate is focused on the aperture drilled in the metal reflective film.

Here, the hole drilled in the metal reflecting film becomes a waveguide having a size smaller than the wavelength, and since the other portions have a size larger than the wavelength, there is no loss of light.

As a result, the near field, i.e., the portion that feels sub-wavelength, is shortened so that the near field is kept farther from the aperture.

Therefore, the near field generation efficiency is improved by about 1000 times or more.

The manufacturing process of the near-field optical head having such a structure is as follows.

3A to 3F are cross-sectional views showing the manufacturing process of the near-field optical head according to the first embodiment of the present invention. First, the silicon substrate 11 is prepared as shown in FIG. 3A, and as shown in FIG. 3B. The lower portion of the silicon substrate 11 is coated with a polymer-based material having different etching properties from silicon (which is less etched than silicon).

Photoresist 12 was used here.

The photoresist 12 is coated and then heat treated to cure the photoresist 12.

Subsequently, as shown in FIG. 3C, the silicon substrate 11 is etched by chemical etching to make holes in the silicon substrate 11.

At this time, the shape of the hole has an inverted trapezoidal shape, in some cases it may be formed in other shapes, such as polygonal, cylindrical.

Here, the base has a size of about 1 to 2 µm, and here it is about 1.5 µm.

This size depends on the laser used, and the shorter the wavelength, the smaller the base.

This size is also optimized to focus on the reflective film.

As shown in FIG. 3D, the reflective film 13 is formed on the entire surface of the substrate 11 including the inverted trapezoidal hole.

Here, the reflective film 13 may be made of aluminum, gold, silver, copper, or other pure metal or two or more alloys as a material having high reflectivity and high thermal conductivity. Gold is used here.

The reflective film 13 having such a material is formed by a method such as sputtering or thermal evaporation.

Subsequently, as shown in FIG. 3E, the photoresist 12 is removed with an organic solvent such as acetone, and then a near field generation hole is formed with a focused ion beam (FIB) at the center of the reflective film 13 formed at the bottom of the inverted trapezoidal hole. To make a near field optical head.

Second embodiment

FIG. 4 is a structural cross-sectional view showing a near-field optical head according to a second embodiment of the present invention. As shown in FIG. 4, a third nonlinear film is formed on a metal reflective film having an aperture, and thus, third nonlinear self-focusing is performed. By using the focusing effect, the laser beam is focused to increase the near field generation efficiency.

5A to 5G are cross-sectional views illustrating a manufacturing process of a near field optical head according to a second exemplary embodiment of the present invention.

5A to 5D are the same manufacturing processes as those of FIGS. 4A to 4D of the first embodiment of the present invention, and thus detailed descriptions thereof will be omitted.

As shown in FIG. 5E, a third order nonlinear film 24 exhibiting self-focusing is formed over the reflective film 23.

Here, the third-order nonlinear material used is capable of knife Kozje arsenide (chalcogenide) based element and a semiconductor element or an alloy thereof such as a-Si, Sb, Ge, InSb, GaAs, ZnSe, AlP, and the SiO ₂ It is also possible to mix a substance in the form of particles into a glass of a matrix.

The thin film having the above material uses a conventional thin film deposition method such as sputtering, thermal evaporation, or CVD.

In addition, as a third tertiary nonlinear substance, a substance having supersaturated absorption properties is also possible.

Here, the supersaturated absorption property is a property that shows high transparency to light of a certain intensity or more, and has a super resolution effect.

Subsequently, after removing the photoresist 12 with an organic solvent such as acetone, as shown in FIG. 5F, only a central portion of the reflective film 23 formed at the bottom of an inverted trapezoidal hole as shown in FIG. 5G is focused on the FIB (Focused Ion). Near-field optical head is manufactured by drilling holes for generating near-field with a beam.

This near-field generating hole is made about 60 nm in diameter at the center of the inverted trapezoid.

The size of this hole is selected between 50 and 100 nm depending on the application range.

The near field optical head and the manufacturing method thereof according to the present invention have the following effects.

According to the present invention, a relatively large hole having a size of about 1 to 2 μm is first formed in a substrate, and then a small hole having a laser wavelength size or less is drilled to about 60 nm and used as an aperture in the metal reflective film formed thereon. Since the near field, that is, the portion that senses the size below the wavelength, is shortened and the near field is kept farther from the aperture, the near field generation efficiency is improved by about 1000 times or more.

Another effect of the present invention is to form a tertiary nonlinear film on the metal reflecting film and use the tertiary nonlinear self-focusing effect to focus the laser beam to increase the near field generation efficiency.

In other words, the near-field generation is improved because the laser beam focused at approximately the wavelength size is focused again by the self-focusing effect and consequently is focused on the aperture.

Claims (10)

A substrate having a first aperture; A reflective film formed on an entire surface of the substrate including the first aperture; And a second aperture formed in a predetermined region of the first aperture, the second aperture being relatively smaller than the first aperture. The near field optical head of claim 1, wherein the first aperture has a wide top surface and a narrow bottom surface. The near field optical head of claim 1, wherein the first aperture is formed in any one of an inverted trapezoid, a polygon, and a cone. The near field optical head according to claim 1, wherein the base of the first aperture is 1 to 2 µm and the second aperture is 50 to 100 nm. The near field optical head according to claim 1, wherein the reflecting film is a metal having good reflectivity and thermal conductivity. 6. The near field optical head according to claim 5, wherein the metal is any one of aluminum, gold, silver, copper, other pure metals, and metal alloys. The near field optical head of claim 1, wherein the reflective film formed on the bottom surface of the first aperture is flat or inclined at a predetermined angle. The near field optical head according to claim 1, wherein a tertiary nonlinear film is formed on the first reflecting film. According to claim 1, wherein the tertiary nonlinear film is a-Si, Sb, Ge, InSb, GaAs, ZnSe, AlP, other chalcogenide-based elements, semiconductor elements, alloys thereof, SiO ₂ as a matrix Near-field optical head, characterized in that any one of the material in the form of particles mixed with the glass, the material having a supersaturated absorption property. Preparing a substrate; Forming an etch stop layer having a different etching property from the substrate on a lower surface of the substrate; Etching a top surface of the substrate to expose the etch stop layer to form a first aperture having a wide top and a narrow bottom; Forming a reflective film on an entire surface of the substrate including the first aperture; Removing the etch stop layer; And forming a second aperture having a smaller size than the first aperture by drilling a hole in a predetermined region of the reflective film formed in the first aperture region.