KR20020093376A - optical disk and method for fabricating the same - Google Patents

Abstract

PURPOSE: An optical disk and a method of manufacturing the optical disk are provided to reduce surface roughness of a reflection layer so as to improve signal quality. CONSTITUTION: An optical disk includes a substrate(10), a plurality of reflection films(11a,11b) stacked on the substrate, an amorphous layer(12) formed between reflection films, a recording layer(13) formed on the reflection films, for recording information, and a protection layer(14) formed on the recording layer. The amorphous layer is formed of one of silicon oxide, Ti-oxide, Cr-oxide, ZnS-SiO2, a compound of them, a Ge-Sb-Te alloy thin film, and Ag-In-Sb-Te alloy thin film. The reflection layer is formed of one of Al, Ag and alloy of Al and Ag.

Description

Optical disk and method for fabricating the same

The present invention relates to an optical disk and a method of manufacturing the same.

In general, phase change type optical disks record the recorded information by irradiating a focused laser beam to a local area of the recording layer to raise / melt it, and rapidly cool it by using a disk structure designed for a rapid diffusion rate of heat to make an amorphous mark at a crystalline base. Clears.

A phase change type optical disc having this principle is usually composed of a simple four-layer film.

That is, it has a four-layer film structure in which a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective heat radiation layer are stacked on a substrate.

It is also possible to have a structure of four or more layers. In this case, four layers can be used as the basis, and other films can be provided between the layers.

At this time, the reflective heat radiation layer is characterized in that the film is formed in the last order in the order of the most constituent layers.

The order of the thin films made in this manner is called normal stacking.

Recently, with the development of high-density recordable media, there has been a trend to increase the numerical aperture of the objective lens of the pickup or to bring the wavelength of the recording light source to the short side in the optical recording apparatus.

However, with increasing the numerical aperture, the distance between the objective lens and the recording layer of the optical recording medium, that is, the working distance becomes short.

In this case, the thickness of the transparent substrate which is present in the intermediate process from the light source to the recording layer should be reduced.

As a result, in the role of a substrate that previously supported the thin film in the normal laminated structure, a progress was made in the form of a thin cover layer covering the multilayer thin film constituting the optical recording medium existing in the path through which the laser passes.

In addition, when increasing the numerical aperture of the lens, there is a problem that the coma abberation due to tilt, which is one of the mechanical fluctuations of the disk, becomes significantly larger in proportion to the third power of the numerical aperture. As the thickness of the substrate located in the path where the laser beam is incident becomes larger, the thickness becomes significantly larger, which is an opportunity to reduce the thickness of the substrate.

In this case, the stacking order of the thin film is reversed stacking, in which the reflective layer is first stacked in reverse order, unlike the normal stacking structure in which the reflective layer is laminated last.

Characteristic in this reverse stacking structure, unlike the normal stacking, the reflective layer must first be formed on the substrate and the other component layers must be stacked.

Then, the cover layer is provided on the upper part of the constituent layer.

Accordingly, the signal characteristics of the medium depend a lot on the surface microstructure of the reflective heat dissipation layer, which is a thin film located at the bottom, unlike the normal stack.

In particular, the focus error signal becomes large in the dynamic driving state of the medium, and consequently, the medium noise is increased.

Accordingly, there is a difficulty in reducing the surface roughness of the recording medium that causes the noise of the medium.

In addition, as a method for lowering the surface roughness of the reflective layer, a method such as ion beam sputtering may be proposed instead of the conventional sputtering, but in this case, there is a problem in that it is not suitable for a mass production process because the time for the process is very long.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems, and to provide an optical disk and a method of manufacturing the same having excellent signal quality by reducing the surface roughness of the reflective layer.

Another object of the present invention is to provide an optical disk and a method of manufacturing the same having excellent productivity in a simple process.

1 is a graph showing the surface roughness at the interface of each layer during normal stacking

2 is a graph showing the surface roughness at the interface of each layer during reversed stacking

3A and 3B are structural cross-sectional views showing optical disks according to the first and second embodiments of the present invention;

4 is a graph showing the surface roughness according to the thickness of the reflective layer of the optical disk

5 is a graph comparing surface roughness of a reflective layer into which an amorphous layer is inserted and a reflective layer into which an amorphous layer is not inserted;

Explanation of symbols for main parts of the drawings

10 substrate 11 reflective layer

12: amorphous layer 13: recording layer

14: protective layer 15: dielectric layer

An optical disk according to the present invention includes a substrate, a reflective layer formed by stacking a plurality of substrates on top of the substrate, an amorphous layer formed between each reflective layer, a recording layer formed on the reflective layer for recording information, and a protective layer formed on the recording layer. It is configured to include.

Here, dielectric layers made of ZnS-SiO ₂ are formed on the upper and lower portions of the recording layer, respectively, and the dielectric layer thickness formed on the recording layer is 50-300 nm and the dielectric layer thickness formed on the lower recording layer is 10-50 nm.

And, the amorphous layer is a metal oxide selected from Si-oxide, Al-oxide, Ti-oxide, Cr-oxide, ZnS-SiO ₂ , mixtures thereof, Ge-Sb-Te alloy thin film, Ag-In-Sb-Te It is made of one of the alloy thin films and has a thickness of 20 to 40Å, and the recording layer is made of (GeTe) _1- x (Sb ₂ Te ₃ ) _x alloy or Ag-In-Sb-Te alloy, and the thickness is 10- It is set to 30 nm.

The reflective layer is made of any one of Al and Ag, or an alloy thereof, and has a thickness of 300 to 550 kPa.

An optical disk manufacturing method according to the present invention comprises the steps of sequentially forming a first reflective layer and an amorphous layer on a substrate, forming a second reflective layer on the amorphous layer, and then a lower dielectric layer, a recording layer, and an upper dielectric layer on the second reflective layer Forming a protective layer over the upper dielectric layer.

At this time, the step of sequentially forming the first reflective layer and the amorphous layer on the substrate may be repeatedly performed in some cases.

As described above, the present invention produced greatly reduces the surface roughness of the reflective layer, thereby realizing an optical recording medium having excellent signal quality, and is capable of forming a multilayer reflective film by a conventional sputtering method, thereby providing excellent productivity.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Referring to the accompanying drawings, preferred embodiments of the present invention having the features as described above are as follows.

FIG. 1 is a graph showing surface roughness at the interface of each layer at normal stacking, and FIG. 2 is a graph showing surface roughness at the interface of each layer at reverse stacking.

In the case of the normal stack as shown in Fig. 1, since the main reflection signals before and after the recording film are detected during recording and reproduction, the surface roughness of the reflection layer does not affect the signal characteristics of the recording medium.

On the other hand, as shown in FIG. 2, the reverse stack has a large signal deterioration due to noise at the time of detecting the recording / reproducing signal due to the large surface roughness of the recording layer due to the surface roughness of the reflective layer.

In other words, the large surface roughness of the recording layer due to the surface roughness of the reflective layer causes the focus error signal to become large in the dynamic driving state of the optical recording medium, thereby increasing the noise of the recording medium.

Therefore, in the present invention, in order to improve the surface roughness of the reflective layer in the reverse stacked structure of the optical disk, one or more amorphous layers are inserted into the reflective layer.

That is, the present invention does not form a reflective layer with a single layer made of Al alloy or the like like a conventional reflective layer, but the unit thickness of the reflective layer is a thin predetermined thickness, while the overall thickness is similar to that of the existing intermediate layer having an amorphous structure when forming a thin film. It is characterized by lowering the surface roughness of the overall multilayer reflective film by inserting one or more layers into the reflective layer.

3A and 3B are structural cross-sectional views showing optical disks according to the first and second embodiments of the present invention, in which FIG. 3A is one case where an amorphous layer is inserted into an intermediate layer in the reflective layer, and FIG. 3B is inserted into the intermediate layer in the reflective layer. This is the case when there are a large number of amorphous layers.

3A and 3B, a plurality of reflective layers 11 are stacked on a polycarbonate substrate 10 having a thickness of about 1.1 mm, and an amorphous layer 12 is formed between each reflective layer 11. A recording layer 13 for recording information is formed on the reflective layer 11 and a protective layer 14 of about 0.1-0.12 m is formed on the recording layer 13.

Here, the dielectric layer 15 is formed above and below the recording layer 13, but in some cases, the dielectric layer 15 may not be formed.

The dielectric layer 15 is formed of ZnS-SiO _2, and the thickness of the dielectric layer 15 formed on the recording layer 13 is about 50-300 nm and the thickness of the dielectric layer 15 formed on the recording layer 13 is about 10. Formed to 50 nm.

In addition, the amorphous layer 12 inserted into the reflective layer 11 includes a metal oxide selected from Si-oxide, Al-oxide, Ti-oxide, Cr-oxide, ZnS-SiO ₂ , a mixture thereof, and Ge-Sb-Te. It is formed of an alloy thin film, Ag-In-Sb-Te alloy thin film, and the like and the thickness is about 20 to 40 kPa, in the embodiment of the present invention is formed to a thickness of about 30 kPa.

The recording layer 13 is formed of a (GeTe) _1-x (Sb ₂ Te ₃ ) _x alloy or an Ag-In-Sb-Te alloy, and has a thickness of about 10-30 nm.

The reflective layer 11 is formed of any one of Al, Ag, or an alloy thereof, and has a thickness of 300 to 550 GPa.

At this time, when only one amorphous layer 12 is inserted into the reflective layer 11 as in the first embodiment of the present invention, the thickness of the reflective layer 11 is formed to about 500 m 3, and a plurality of amorphous layers are formed as in the second embodiment of the present invention. When the layer 12 is inserted into the reflective layer 11, the thickness of the reflective layer 11 is about 330 mm 3.

Referring to the manufacturing process of the present invention formed in such a structure as follows.

As shown in FIG. 3A, first, the first reflective layer 11a and the amorphous layer 12 are sequentially formed on the substrate 10 by the conventional sputtering method, and the second reflective layer 11b is formed on the amorphous layer 12. do.

In this case, when the plurality of amorphous layers 12 are inserted as shown in FIG. 3B, the process is repeated to sequentially form the second reflective layer 11b and the second amorphous layer 12b on the first amorphous layer 12a. The third reflective layer 11c is formed on the second amorphous layer 12b.

Subsequently, the lower dielectric layer 15, the recording layer 13, and the upper dielectric layer 15 are sequentially formed on the second or third reflective layers 11b and 11c, and then about 0.1-0.12 m using an ultraviolet curable resin thereon. By attaching the protective layer 14 to a degree, an optical disk is produced.

FIG. 4 is a graph showing surface roughness according to the thickness of the reflective layer of the optical disk, and as shown in FIG. 4, it can be seen that the surface roughness increases linearly as the thickness of the reflective layer is increased.

However, the present invention does not constitute a single layer of the reflective layer, but stacks a plurality of unit reflective layers having a thin thickness and inserts an amorphous layer having a thin thickness therebetween, thereby reducing the thickness of the reflective layer as a whole to improve surface roughness.

5 is a graph comparing surface roughness of a reflective layer into which an amorphous layer is inserted and a reflective layer into which an amorphous layer is not inserted.

Here, type 1 is a case where only one amorphous layer of about 100 mV is inserted between the reflective layers of about 1000 mW, and type 2 is a case where two amorphous layers of about 100 mV are inserted between the reflective layers of about 1000 mW.

As shown in FIG. 5, the surface roughness of the reflective layer of 1000 μs without the amorphous layer is about 23 A, whereas the surface roughness of the reflective layer having the amorphous layer inserted into the intermediate layer is slightly different depending on the type of the amorphous layer. It can be seen that the surface roughness decreases rapidly.

As such, the reason why the surface roughness of the reflective layer decreases is that the column structure is formed as the reflective layer grows, and the coarse column is formed by mutual coupling between these columns, thereby increasing the surface roughness. do.

In other words, such surface roughness can be considered in terms of grain growth of general phase transformation theory.

Therefore, such coarse columnar structure is a cause for increasing surface roughness.

On the contrary, when the amorphous layer is inserted into the reflective layer, column growth due to continuous growth is prevented, and since the new crystal layer is newly formed on the surface of the amorphous layer, the surface roughness of the final reflective layer is greatly reduced.

The optical disk according to the present invention can realize an optical disk having excellent signal quality by inserting an amorphous layer inside the reflective layer to reduce the surface roughness of the reflective layer, and is excellent in productivity because a multilayer reflective layer is formed by a conventional sputtering method. .

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (6)

Board; A reflective layer formed by stacking a plurality of substrates on the substrate; An amorphous layer formed between each reflective layer; A recording layer formed on the reflective layer to record information; And, And a protective layer formed on the recording layer. The method of claim 1, wherein the amorphous layer is a metal oxide selected from Si-oxide, Al-oxide, Ti-oxide, Cr-oxide, ZnS-SiO ₂ , mixtures thereof, Ge-Sb-Te alloy thin film, Ag- An optical disk comprising any one of In-Sb-Te-based alloy thin films and having a thickness of 20 to 40 microseconds. The optical disk according to claim 1, wherein the recording layer is made of a (GeTe) _1-x (Sb ₂ Te ₃ ) _x alloy or an Ag-In-Sb-Te alloy system, and has a thickness of 10 to 30 nm. The optical disk according to claim 1, wherein the reflective layer is made of any one of Al and Ag or an alloy thereof, and has a thickness of 300 to 550 kPa. Sequentially forming a first reflective layer and an amorphous layer on the substrate; Forming a second reflective layer over the amorphous layer; Sequentially forming a lower dielectric layer, a recording layer, and an upper dielectric layer on the second reflective layer; And, And forming a protective layer on the upper dielectric layer. 6. The method of claim 5, wherein sequentially forming the first reflective layer and the amorphous layer on the substrate is repeatedly performed.