KR20020083760A - Thin film optical disc - Google Patents

Abstract

PURPOSE: A thin film optical disc is provided to reduce the surface roughness and the signal noise by using a mixture film of Al and SiO2 as a reflecting layer in a thin film optical disc of a reversed stacking structure. CONSTITUTION: A thin film optical disc includes a reflecting layer(20), an upper dielectric protecting layer(30), a recording layer(40), and a lower dielectric protecting layer(50) stacked on a poly carbonate substrate(10) in sequence, wherein the reflecting layer is formed of one of Al, Al alloy, Ag or Ag alloy added with a predetermined amount of oxide or nitride, and the amount of the oxide or nitride is 0.1-10mole%.

Description

Thin film optical disc

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thin film optical discs, and more particularly to thin film optical discs for reducing signal noise by reducing the surface roughness of the reflective layer in a reverse stacked structure used for thin cover films.

Recently, as the DVD (Digital Versatile Disc) standard is proposed and standardized, various products such as DVD-ROM, DVD-RAM, DVD-R, DVD-RW, and DVD + RW have been released.

These DVD products are based on a single-sided single layer and have a capacity of about 4.7 gigabytes (GB). This is the capacity to store about two hours of movies in VHS quality, and is expected to expand gradually.

These optical storage media are two disks each having a thickness of 0.6 mm, which is 1.2 mm in diameter, 12 cm in diameter, and contains information (i.e., a reflective layer or a multilayer thin film). It is composed of a laminated substrate of 0.6mm and an adhesive (adhesive) layer for bonding the two substrates to each other.

In the above optical information storage medium, in order to record information or to read information on the medium, in principle, the laser beam leaving the optical pick-up objective lens has a constant thickness (for example, 0.6 in 4.7 GB DVD). passing through the transparent substrate of mm) and incident on the information recording layer (or information storage layer).

In this case, the size of the spot in the information storage layer determining the recording density of the recording medium is proportional to the wavelength of the light source used and inversely proportional to the numerical aperture of the objective lens.

Therefore, in order to increase the information recording density, it is necessary to use a short wavelength light source and a lens having a large numerical aperture for a given substrate thickness.

However, when increasing the numerical aperture of the lens, the comma aberration due to the tilt of the disk is proportional to the third power of the numerical aperture. There is a problem that is significantly larger.

In particular, the degree of occurrence of coma aberration is remarkable as the thickness of the substrate positioned in the incident light direction becomes thicker.

In addition, when a thick substrate is used, the duration of signal degradation caused by dust or the like on the surface of the substrate is extended, which greatly affects the focus control or tracking control.

As a result, the introduction of a short wavelength LD (Laser Diode), a high numerical aperture (NA) objective lens and a thin cover layer has been proposed in a storage medium having a high recording capacity of about 20GB or more per disc.

However, despite the fact that the thin film technology can minimize the occurrence of high density, transmission speed, and coma aberration, one of the major obstacles to practical use is the increase in signal noise due to the reversed stacking thin film structure.

Among the thin films constituting the optical disk, an aluminum (Al) film is applied in a crystalline state, compared with an amorphous state due to heterogeneous nucleation and grain growth characteristics. The surface roughness is large. Usually, the Al thin film has an RMS roughness of 20 to 30 A at a film thickness of 100 nm.

Therefore, the aluminum (Al) film is composed of many grains and grain boundaries, and thus has a large surface roughness compared to other thin films applied in an amorphous state.

That is, although there is a difference depending on the thickness of the thin film, the aluminum (Al) thin film has a root mean square (RMS) roughness of about 20 to 30A.

On the other hand, the dielectric layers ZnS-SiO ₂ or GeSbTe are applied in an amorphous state, and because there is no grain, the surface roughness is very small as 2 ~ 10A.

In general optical discs, films are stacked on the substrate in the order of dielectric layer / recording layer / dielectric layer / reflective layer, and the signal is detected to be reflected from the recording layer. Therefore, the large surface roughness of the reflective layer does not affect the detected signal.

However, in order to form a thin cover film to increase the recording density of the recording medium, reversed stacking must be performed. That is, a film should be laminated on the substrate in the order of a reflective layer, a dielectric layer, a recording film layer, and a dielectric layer.

At this time, since the aluminum layer, which is a reflective layer, is applied first, the dielectric layer and the recording film layer applied thereon are affected by the large surface roughness of aluminum.

That is, the surface roughness of the reflective layer is very large (about 25 A) while the surface roughness of the recording layer is very small (2 A or less) in a general optical disc in which films are laminated in the order of dielectric layer / recording film layer / dielectric layer / reflective layer on a substrate as shown in FIG.

However, in the reverse stacked optical disc in which films are stacked in the order of the reflective layer / dielectric layer / recording film layer / dielectric layer on the substrate as shown in FIG. 2, it is understood that the surface roughness of the recording layer is very large at about 15A at about 25A as in FIG. Can be.

Therefore, residual noise is generated in the detected signal due to the large surface roughness of the recording film layer, and the jitter value is worsened, resulting in poor recording characteristics.

To reduce this noise, the surface roughness of the aluminum (Al), aluminum alloy, silver (Ag), and silver alloy layer used as the reflective layer must be lowered.

As a method, a small amount of titanium (Ti), chromium (Cr), or the like is added to the reflective layer, an etching method after aluminum sputtering, or a method using ion beam sputtering rather than DC sputtering is used.

However, the method of forming the reflective layer of the thin film optical disc according to the related art described above has the following problems.

First, the method of adding a small amount of titanium (Ti), chromium (Cr) and the like is very small.

Secondly, etching after aluminum sputtering, or using ion beam sputtering rather than DC sputtering, takes longer processing time and is not in-line production, resulting in poor productivity. There is a problem that is not suitable for mass production.

Accordingly, an object of the present invention is to solve the above problems, and to reduce the surface roughness of the reflective film in the thin film optical disc having an inverse stacking structure, thereby minimizing signal noise on the optical disc drive.

1 is a view showing the surface roughness of each interface in a laminated structure of a general disk

2 is a diagram showing the surface roughness of each interface in a laminated structure of a general thin cover film disk;

3 is a view showing the structure of a thin film optical disk according to the present invention;

4 is a view showing the surface roughness according to the amount of SiO ₂ added to the reflective film according to the present invention

* Explanation of symbols for main parts of the drawings

10 substrate 20 reflective layer

30, 50: dielectric protective layer 40: recording layer

60: cover film

A thin film optical disc according to the present invention for achieving the above object is a thin film optical disc in which a reflective layer, an upper dielectric protective layer, a recording layer, and a lower dielectric protective layer are sequentially stacked on a substrate, wherein the reflective layer is aluminum (Al). A certain amount of SiO ₂ is added to one of aluminum alloy, silver (Ag) and silver alloy (Ag alloy).

Another feature of the thin film optical disk according to the present invention for achieving the above object is a substrate, and any one of aluminum (Al), aluminum alloy (Al alloy), silver (Ag) or silver alloy (Ag alloy) on the substrate. And a reflective layer formed with a predetermined amount of SiO ₂ having a thickness of 30 to 300 nm, and ZnS-SiO ₂ , SiO ₂ , SiN, (Zr _x Ce _1-x ) _y O _1-y , AlN, Al ₂ on the reflective layer. A first dielectric protective layer formed of any one of O ₃ having a thickness of 10 to 50 nm, a recording layer formed of a GeTe-Sb ₂ Te ₃ material having a thickness of 10 to 30 nm on the first dielectric protective layer; A second dielectric protection layer having a thickness of 50 to 300 nm formed of any one of ZnS-SiO ₂ , SiO ₂ , SiN, (Zr _x Ce _1-x ) _y O _1-y , AlN, and Al ₂ O ₃ on the recording layer. It is composed of layers.

In this case, the amount of SiO ₂ added is 0.1 to 10 mol%, but there is another feature.

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.

A preferred embodiment of a thin film optical disc according to the present invention will be described with reference to the accompanying drawings.

3 is a view showing the structure of a thin film optical disk according to the present invention.

Referring to FIG. 3, the reflective layer 20, the upper dielectric protective layer 30, the recording layer 40, and the lower dielectric protective layer 60 are sequentially stacked on the polycarbonate substrate 10 having a thickness of 1.1 mm.

And a thin cover film 60 of 0.1 mm is attached thereon using an adhesive.

At this time, the reflective layer 20 is used by adding 0.1 to 10 mol% of SiO ₂ to aluminum (Al), aluminum alloy (Al alloy), silver (Ag) or silver alloy (Ag alloy). This is because the surface roughness of the reflective layer 20 is reduced as the amount of SiO ₂ added increases.

FIG. 4 is a view showing surface roughness that changes as the amount of SiO ₂ added to aluminum increases. As shown in FIG. 4, the surface roughness decreases as the amount of SiO ₂ increases.

Next, the dielectric protective layers 30 and 50 mainly use ZnS-SiO ₂ , and in addition, SiO ₂ , SiN, (Zr _x Ce _1-x ) _y O _1-y , AlN, Al ₂ O ₃ , and the like. You may use it.

The recording layer 30 uses a conventional GeTe-Sb ₂ Te ₃ material.

The thin film optical disc manufacturing method according to the present invention configured as described above is as follows.

Joining the polycarboxylic carbonate substrate 10, an inert gas ion containing argon (Ar) by the DC or RF magnetron (magnetron) sputter techniques turning on the aluminum alloy _{-SiO 2, ZnS-SiO 2,} GeSb-Sb 2 Te 3 target The film is formed in order by the predetermined production pressure and the production power.

At this time, the thickness of each layer of each reflective layer 20 of aluminum -SiO ₂ layer is 30 ~ 300nm, an upper protective layer 20, a ZnS-SiO ₂ dielectric layer is 10 ~ 50nm, the phase-change type recording reproduction layer 30 The GeSb-Sb ₂ Te ₃ layer is 10-30 nm, and the lower protective layer 50, the ZnS-SiO ₂ dielectric layer, is about 50-300 nm.

And a thin cover film 60 is adhered on it.

In particular, the aluminum-SiO ₂ layer, which is the reflective layer 20, is co-sputtered using Al-SiO ₂ targets or aluminum and SiO ₂ targets, respectively.

As described above, the thin film optical disk according to the present invention uses a mixed film of aluminum (Al) and SiO _{2 as} a reflective layer, thereby significantly reducing surface roughness and reducing signal noise.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the 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 (2)

In a thin film optical disc in which a reflective layer, an upper dielectric protective layer, a recording layer, and a lower dielectric protective layer are sequentially stacked on a substrate, The reflective layer is a thin film optical disc, characterized in that a certain amount of oxide or nitride is added to any one of aluminum (Al), aluminum alloy (Al alloy), silver (Ag) or silver alloy (Ag alloy). The method of claim 1, The amount of the oxide or nitride is added is a thin film optical disk, characterized in that 0.1 to 10 mol%.