HK1097343B - High density readable only optical disc and method of preparing the same - Google Patents

Description

High-density read-only optical disc and its preparing method

This application claims the benefit of korean patent application No. 2003-65534 filed by the korean intellectual property office at 9/22/2003, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a high-density read-only optical disc which allows reading of marks having a size not greater than a reading resolution limit of a laser beam by using a super-resolution near-field structure located within the disc, and a method of manufacturing the same.

Background

Since the recording area required per recording unit of an optical disc is smaller than that of a conventional magnetic recording medium, the optical disc is widely used as a high-density recording medium. Optical discs are classified into Read Only Memory (ROM) discs, which allow only reading of information recorded thereon, Write Once Read Many (WORM) discs, which allow only recording of information thereon once, and rewritable discs, which allow erasing of information thereon and re-recording of information thereon, according to their properties.

Recordable compact discs (CD-R) are examples of WORM optical discs. The CD-R includes a recording layer containing an organic dye such as cyanine, phthalocyanine, or the like. A recording laser having a wavelength of 780nm is irradiated onto the recording layer to decompose the dye layer, and a recorded signal can be read with a power supply of 1mW or less. The CD-R has a recording capacity of about 650MB, and is widely used for recording and reading various types of data such as text data, music, images, and the like.

However, optical recording media such as CD-R or rewritable compact disc (CD-RW) using a recording laser beam having a wavelength of 780nm have insufficient capacity for storing moving images, and thus, they cannot be used in a complicated multimedia environment.

In order to solve the above problems, a Digital Versatile Disc (DVD) having a capacity of 2.7-4.7GB using a short-wave laser beam of 630-. DVDs are also classified into read-only DVDs (DVDs), write-once read-many DVDs (DVD-R), and rewritable DVDs (DVD-RAM, DVD + RW, DVD-RW).

With the DVD-R, a laser beam is irradiated onto the recording layer to transform and decompose the recording layer, thereby recording data. With DVD-RAM and DVD-RW, data is recorded by causing a change in optical properties by a change in phase. Since the DVD-R using the organic dye is more advantageous than other media in terms of compatibility with the DVD-ROM, price and capacity, research has been focused on developing the DVD-R.

With respect to many media that have been recently developed, the greatest concern is capacity, and various methods for increasing capacity are under development. The capacity of an optical disc depends mainly on how many accurately reproducible small pits can be formed in a fixed area and the performance of a laser beam capable of accurately reading these pits. Although the light emitted from the laser diode is condensed by the objective lens, the light is not condensed into an infinitely small spot, but forms a beam having a finite width, which is called a diffraction limit. In a general optical disc, when the wavelength of the light source is λ and the numerical aperture of the objective lens is NA, λ/4NA represents a reading resolution limit. Therefore, when the wavelength of the light source is shortened or the numerical aperture of the objective lens is increased, the recording capacity is increased. However, current laser technology cannot provide laser light of short wavelengths, and the cost of manufacturing an objective lens with an increased numerical aperture is relatively high. In addition, since the numerical aperture of the objective lens is increased, the working distance between the pickup and the disc is reduced to some extent, and the surface of the disc may be damaged due to collision of the pickup with the disc. As a result, data is lost.

Fig. 1 is a graph showing a relationship between a pit length and a carrier to noise ratio (CNR) in a conventional read-only optical disc having a silver reflective layer formed on a substrate. As is clear from fig. 1, when the pit length is not less than 290nm, the CNR is 40dB or more, and information recorded as pits can be read smoothly. However, when the pit length is less than 290nm, the CNR drops sharply. In other words, the CNR is 16dB when the pit length is 265nm, and is close to 0 when the pit length is 250nm or less.

In order to overcome the reading resolution limit, research is now being conducted to find optical discs having a super-resolution near-field structure (hereinafter referred to as "super-resolution structure"). Such an optical disc is mainly used for an optical disc using a phase change recording method, but may be used for a read-only disc. Regarding the super-resolution structure, a special mask layer is formed in the optical disc, and Near Field Reading (NFR) is enabled by surface plasmon (plasmon) generated in the mask layer when information is read. Therefore, the problem of the reading resolution limit is overcome, so that very small recording marks can be read.

Metal oxides such as silver oxide are used for mask layers in recordable optical discs, and metal oxides or fine metal particles are used for mask layers in read-only optical discs.

Fig. 2 is a graph showing CNR properties with respect to pit (mark) depth of a read-only optical disc using a super-resolution structure. Referring to fig. 2, in the case where the pit length is not more than the reading resolution limit, the CNR property is better for a disc with a pit depth of 50nm than for a disc with a pit depth of 100 nm. However, in the case where the pit length is not less than the reading resolution limit, the CNR property is better for a disc with a pit depth of 100nm than for a disc with a pit depth of 50 nm. This shows that effective CNR properties can be obtained only when the pit depths differ with respect to the pit lengths. However, in the conventional read-only optical disc, since the pit depth cannot be adjusted according to the pit length when an original plate (original plate) of the disc is manufactured by conventional optical etching or electron beam etching, the pit depth is uniform regardless of the pit length.

Drawings

These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a graph showing a relationship of a pit length to a carrier to noise ratio (CNR) in a conventional read-only optical disc;

fig. 2 is a graph showing the CNR properties based on pit depth of a read-only disc using a super-resolution structure of an embodiment of the present invention;

fig. 3 is a schematic view of an optical disc according to an embodiment of the present invention, in which a mask layer is formed on a transparent substrate having pits with different depths according to pit lengths;

fig. 4 is a schematic view showing a mechanism of forming a pit by irradiating a laser beam onto a substrate when a volume expansion layer is composed of TbFeCo;

fig. 5 to 7 show Atomic Force Microscope (AFM) photographs of a master plate of an optical disc prepared according to another embodiment of the present invention.

Technical problem

The present invention provides a high-density read-only optical disc that allows reading of pits having a size not greater than the limit of reading resolution and having different pit depths according to pit lengths.

The present invention also provides a method of manufacturing a high-density read-only optical disc.

Technical scheme

According to an aspect of the present invention, there is provided a high-density read-only optical disc including: a substrate having pits of different lengths according to unit information, wherein the depth of the pit increases as the pit length increases; a mask layer comprising a mixture of metal oxide or fine metal particles and a dielectric material.

According to another aspect of the present invention, there is provided a method of manufacturing a high-density read-only optical disc, the method including: irradiating a laser beam onto a master of an optical disc, wherein a substrate, a first dielectric layer, a volume expansion layer, and a second dielectric layer are sequentially formed as a function of irradiation time, the volume expansion layer including an alloy or a metal oxide of a rare earth metal and a transition metal; expanding the volume expansion layer by irradiation of a laser beam to form pits having different lengths and depths on the second dielectric layer; plating the base plate with a metal to form a mold; separating the mold; injection molding the substrate using a mold; a mask layer is formed on a substrate, the mask layer comprising a metal oxide or a mixture of fine metal particles and a dielectric material.

Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Advantageous effects

As described above, the high-density read-only optical disc according to an embodiment of the present invention can be used to read pits not greater than the reading resolution limit and can obtain an optimal CNR since the pit depth varies according to the pit length. Also, the method of manufacturing a high-density read-only optical disc according to another embodiment of the present invention can be used to manufacture a high-density read-only optical disc having an optimum pit depth based on a pit length.

Detailed Description

Now, the present invention will be described in more detail.

The high-density read-only optical disc according to an embodiment of the present invention is characterized in that pits formed on a substrate have different lengths, and pit depths are different according to the pit lengths. In other words, the pit depth is larger as the pit length is larger, and the pit depth is smaller as the pit length is smaller, so that the optimum CNR property is obtained according to each pit length.

Fig. 3 illustrates an optical disc according to an embodiment of the present invention, in which a mask layer 11 is formed on a transparent substrate 10 having pits 17 of different depths according to pit lengths.

The substrate 10 contains a material selected from materials having high transparency, effective pressure resistance, heat resistance, environmental resistance, and the like in the wavelength range of the recording laser beam, and such a material can be molded by a conventional method of preparing a substrate, such as injection molding. Examples of such materials include polycarbonate, polymethylmethacrylate, epoxy, polyester, amorphous polyolefin, and the like.

The mask layer 11 may be composed of a metal oxide or a mixture of fine metal particles and a dielectric material. The metal oxide can be PtO_X、PdO_X、AuO_X、AgO_X、WO_XOr mixtures thereof. When a metal oxide is used as a mask layer, the metal oxide is decomposed into fine metal particles and oxygen, forming surface plasmon, thereby obtaining the effect of the super-resolution structure. Since the power of the laser beam used during reading is not sufficient to decompose the metal oxide, surface plasmons are not formed. However, a small amount of the metal particles 16 in a reduced state may be present in the mask layer 11, so that the reduced metal particles 16 serve as a source of surface plasmon.

Meanwhile, when a mixture of fine metal particles and a dielectric material is used as a mask layer, the fine metal particles are dispersed in the dielectric material and can be directly used as a source of surface plasmon.

The dielectric material used in the mask layer is an oxide, nitride, sulfide or fluoride of a metal or a mixture thereof, and examples of such materials include SiO, Al₂O₃、Si₃N₄、SiN、ZnS、MgF₂And the like. Rare metals such as gold, platinum, rhodium, palladium, and the like can be used as the metal material dispersed in the mask layer. No chemical reaction occurs between the dielectric material and the metal material, so the fine metal particles can maintain their shapes.

Although not shown in fig. 3, the optical disc according to an embodiment of the present invention may further include Sb or Sb-containing between the substrate 10 and the mask layer 11₂Te₃The crystalline read assist layer. The crystal reading assist layer is formed to improve the effect of the super-resolution structure while providing high reflectivity during reading, and is directly crystallized after being formed as a thin film.

Also, the optical disc according to an embodiment of the present invention may further include a reflective layer for providing high reflectivity during recording or reading. The reflective layer may be composed of a metal having high thermal conductivity and high reflectivity to prevent the layer from rapidly changing. Accordingly, the reflective layer contains a metal selected from the group consisting of Au, Al, Cu, Cr, Ag, Ti, Pd, Ni, Zn, Mg and alloys thereof, and is formed to a thickness of 50 to 150nm by a general method such as vacuum deposition, electron beam or sputtering. In order to ensure sufficient reflectivity and reliability, the thickness of the reflective layer may be 60-120 nm.

The optical disc according to an embodiment of the present invention may further include a dielectric layer between the mask layer and the substrate, between the mask layer and the reflective layer, or on both sides of these layers. The dielectric layer between the mask layer and the substrate prevents the substrate from being damaged by heat, and the dielectric layer between the mask layer and the reflective layer serves as a diffusion preventing layer (diffusion).

The dielectric substance used in the dielectric layer is an oxide, nitride, sulfide or of a metalFluorides or mixtures thereof, examples of these substances including SiO₂、Al₂O₃、Si₃N₄、SiN、ZnS、MgF₂And the like.

The optical disc according to an embodiment of the present invention may further include a protective layer to protect other layers of the optical disc. The protective layer may be formed by a conventional method, for example, by spin-coating an epoxy resin or an acrylate UV-curable resin having high impact strength and being transparent on the reflective layer and then curing the coating layer with UV rays.

A method of manufacturing a high-density read-only optical disc according to another embodiment of the present invention includes: irradiating a laser beam onto a master of an optical disc, wherein a substrate, a first dielectric layer, a volume expansion layer, and a second dielectric layer are sequentially formed as a function of irradiation time, the volume expansion layer being composed of an alloy or a metal oxide of a rare earth metal and a transition metal; expanding the volume expansion layer by irradiation of a laser beam to form pits having different lengths and depths on the second dielectric layer; plating the base plate with a metal to form a mold; separating the mold; injection molding the substrate using a mold; a mask layer comprising a metal oxide or a mixture of fine metal particles and a dielectric material is formed on a substrate.

In this method, when a laser beam is irradiated onto the original plate, a portion of the volume-expanding layer onto which the laser beam has been irradiated is heated, so that the temperature of this portion rises. At this time, the temperature of the heating region has a gaussian distribution, and the temperature of the central portion of the laser beam spot is the highest. When the temperature is higher than a specific critical temperature, thermal change occurs, and pits are formed. Since the thermal variation occurs in the central portion of the laser beam spot, the diameter of the pit is much smaller than that of the laser beam spot.

Fig. 4 shows a mechanism of forming pits when a radiation laser beam is irradiated onto the volume expansion layer of TbFeCo. That is, when a laser beam is irradiated onto the volume expansion layer of TbFeCo, heat is generated in the irradiated portion, so that TbFeCo is diffused into the dielectric layer, or a substance (i.e., S) of the dielectric layer is diffused into TbFeCo, or TbFeCo forms a compound with the dielectric substance in a portion heated to a temperature higher than a critical temperature by the generated heat. Due to the volume expansion of the compound formed at this time, pits are formed in the second dielectric layer. The critical temperature of TbFeCo is about 350 ℃.

Meanwhile, when the volume expansion layer contains a metal oxide such as PtO_X、PdO_X、AuO_X、AgO_XOr WO_XAt this time, oxygen is generated in the portion of the volume expansion layer heated by the irradiated laser beam, so that the volume expands to form a pit.

The glass substrate 20 is generally used as a master for an optical disk. The glass substrate 20 is polished and rinsed, and then a first dielectric layer 24, a volume expansion layer 25, and a second dielectric layer 26 are sequentially formed on the glass substrate 20 by sputtering or the like. Meanwhile, the information recorded in the original is edited in advance by an editor as information to be written in the substrate 10 of the optical disc. The edited information is emitted through the signal emitting device, and thus, the irradiation time of the laser beam is adjusted to form pits having different lengths and depths. Then, an electrode for a plating process is applied to the resulting original plate, and the metal is plated to form a mold. Then, the mold is separated. Finally, a mold prepared by a mastering process is used to injection mold polycarbonate, and the like. As a result, the substrate used in the optical disc according to the embodiment of the present invention was obtained.

Fig. 5 to 7 show AFM pictures of a master plate of an optical disc prepared according to another embodiment of the present invention. The left drawing is a top picture, and the right drawing is a cross-sectional view of a portion indicated by a chain line in the left drawing. The laser beam used had a wavelength of 405nm and a Numerical Aperture (NA) of 0.65. In fig. 5, a pattern having a pulse frequency of 15MHz, a pit diameter of about 100nm, and a pit depth of about 65nm was formed.

Also, in fig. 6, a pattern with a pulse frequency of 18.75MHz, a pit diameter of about 80nm, and a pit depth of about 45nm was formed, and in fig. 7, a pattern with a pulse frequency of 30MHz, a pit diameter of about 50nm, and a pit depth of about 35nm was formed. From the above results, it is clear that the pit depth increases as the pit length increases. Therefore, the pit depth increases when the pit length is larger than the reading resolution limit, and the pit depth decreases when the pit length is smaller than the reading resolution limit, thereby obtaining the optimum CNR property in each case.

The present invention will be described in more detail with reference to the following examples. The following examples are for illustrative purposes and are not intended to limit the scope of the present invention.

Example 1

1- (1) preparation of optical disk substrate

ZnS-SiO with a thickness of 170nm was formed on a circular glass substrate with a thickness of 6mm by sputtering₂The layer is used as a first dielectric layer, a TbFeCo layer with the thickness of 15nm is formed as a volume expansion layer, and ZnS-SiO with the thickness of 15nm is formed₂The layer was used as a second dielectric layer, and then an original plate of an optical disk in which a track pitch was 0.74 μm and pits having different pit depths were formed according to the pit length in a range from a pit depth of 50nm when the minimum pit length was 200nm to a pit depth of 440nm when the maximum pit length was 680nm was prepared with a laser having a Numerical Aperture (NA) of 0.65. An electrode for an electroplating process is applied to the resulting substrate, and then, nickel is electroplated to form a mold. Next, the mold is separated. Finally, a mold prepared by a mastering process was used to injection mold polycarbonate, thereby preparing a substrate of an optical disc having a thickness of about 0.6 mm.

1- (2) preparation of optical disks

ZnS-SiO is respectively applied with 400W and 160W power supplies₂The target and the Pt target were co-sputtered on the substrate prepared as in 1- (1) above to form a mixed thin film having a thickness of about 50 nm. At this time, Ar was supplied at a rate of 20sccm, and the deposition pressure was 1.5 mTorr, ZnS-SiO₂The volume ratio to Pt was 80: 20.

Example 2

ZnS-SiO formation on the substrate of the optical disk prepared in example 1- (1) by sputtering₂The layer is used as a dielectric layer to form ZnS-SiO₂+ Pt layer as mask layer, then sputteringAg with a thickness of about 100nm forms a reflective film. Next, a photo-curable resin protective layer was formed by spin coating, thereby completing the optical disc. Here, ZnS-SiO was co-sputtered by power supplies of 400W and 160W, respectively₂Target and Pt target form ZnS-SiO₂The mixed layer with Pt was used as a mask layer, thereby forming a mixed thin film having a thickness of 50 nm. Ar is supplied at a rate of 20sccm at a deposition pressure of 1.5 mTorr, ZnS-SiO in thin film₂And Pt were in a volume ratio of 80: 20.

Example 3

Sb was sputtered as a crystal reading aid layer on the substrate of the optical disk prepared in (1) in example 1 to form a thin film having a thickness of about 50nm, and then ZnS-SiO was formed by sputtering₂The layer serves as a first dielectric layer. Thereafter, argon and oxygen were injected into the vacuum vessel, and a Pt target was sputtered to form PtO having a thickness of about 3.5nm_XA mask layer.

Test example 1

The performance of the discs obtained in examples 1 to 3 was evaluated on a DVD evaluation apparatus with a laser having a wavelength of 635nm and a pickup having an NA of 0.60. The linear velocity was 2m/s and the read power was 2 mW. In this case, the reading resolution limit (λ/4NA) is 265nm, and the minimum pit length in the DVD is 400 nm. In the optical discs prepared in examples 1 to 3, a CNR of about 40dB or more was obtained with respect to a pit having a length of about 150nm, which is a typical value actually used. From the above results, it was confirmed that the optimum CNR can be obtained by adjusting the pit depth according to the pit length.

As described above, the high-density read-only optical disc according to an embodiment of the present invention can be used to read pits not greater than the reading resolution limit and can obtain an optimal CNR since the pit depth varies according to the pit length. In addition, the method of manufacturing a high-density read-only optical disc according to another embodiment of the present invention can be used to manufacture a high-density read-only optical disc having an optimum pit depth according to a pit length.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims (31)

1. A high-density read-only optical disc comprising:

a substrate having a plurality of pits that differ in length according to unit information, wherein a depth of a pit of the plurality of pits increases as a pit length of the pit increases;

a mask layer, comprising:

a metal oxide, or

A mixture of fine metal particles and a dielectric material.

2. Such as rightThe high-density read-only optical disc of claim 1, wherein the metal oxide is PtO_X、PdO_X、AuO_X、AgO_X、WO_XOr mixtures thereof.

3. The high-density read-only optical disc of claim 1, wherein the fine metal particles are gold, platinum, rhodium, palladium, or a mixture thereof.

4. The high-density read-only optical disc of claim 1, wherein the dielectric material is an oxide, nitride, sulfide, or fluoride of a metal or a mixture thereof.

5. The high-density read-only optical disc of claim 1, wherein the dielectric material is ZnS-SiO₂。

6. The high-density read-only optical disc of claim 1, further comprising a layer of Sb or Sb between the substrate and the mask layer₂Te₃A crystalline read assist layer of composition.

7. The high-density read-only optical disc of claim 1, further comprising a dielectric layer on at least one surface of the mask layer, the dielectric layer comprising a metal oxide, nitride, sulfide, or fluoride, or a mixture thereof.

8. The high-density read-only optical disc of claim 7, wherein the dielectric layer is made of ZnS-SiO₂And (4) forming.

9. The high-density read-only optical disc of claim 1, further comprising a reflective layer on the mask layer.

10. The high-density read-only optical disc of claim 9, wherein the reflective layer comprises a metal selected from the group consisting of Au, Al, Cu, Cr, Ag, Ti, Pd, Ni, Zn, Mg, and alloys thereof.

11. The high-density read-only optical disc of claim 9, wherein the reflective layer is formed to have a thickness of 50-150 nm.

12. The high-density read-only optical disc of claim 11, wherein the reflective layer is formed to have a thickness of 60-120 nm.

13. A method of preparing a high-density read-only optical disc, the method comprising:

irradiating a laser beam onto a master plate of an optical disc and adjusting an irradiation time of the laser beam, wherein the master plate of the optical disc is sequentially formed with a substrate, a first dielectric layer, a volume expansion layer, and a second dielectric layer, wherein the volume expansion layer includes an alloy or a metal oxide of a rare earth metal and a transition metal;

expanding the volume expansion layer by irradiation of a laser beam to form pits having different lengths and depths on the second dielectric layer;

plating the original plate with a metal to form a mold;

separating the mold;

injection molding the substrate using the mold;

forming a mask layer on the substrate, the mask layer comprising:

a metal oxide, or

Fine metal particles and dielectric materials and mixtures.

14. The method of claim 13, wherein the alloy of rare earth and transition metals is TbFeCo, and the volume of the volume-expanding layer is altered by interdiffusion with a dielectric layer or by a chemical change induced by heating.

15. As claimed inThe method of claim 13, wherein the metal oxide is PtO_X、PdO_X、AuO_X、AgO_XOr WO_XAnd changing the volume of the volume expansion layer by heating to release oxygen.

16. The method of claim 13 wherein the depth of the pits increases as the length of the pits formed increases.

17. The method of claim 13, further comprising forming Sb or Sb between the substrate and the mask layer₂Te₃A crystalline read assist layer of composition.

18. A high-density read-only optical disc comprising:

a transparent substrate having a plurality of pits that differ in length according to unit information, wherein a depth of a pit of the plurality of pits increases as a pit length of the pit increases;

a mask layer comprising:

a metal oxide, or

A mixture of fine metal particles and a dielectric material.

19. The high-density read-only optical disc of claim 18, wherein the metal oxide is PtO_X、PdO_X、AuO_X、AgO_X、WO_XOr mixtures thereof.

20. The high-density read-only optical disc of claim 18, wherein the fine metal particles are gold, platinum, rhodium, palladium, or a mixture thereof.

21. The high-density read-only optical disc of claim 18, wherein the dielectric material is an oxide, nitride, sulfide, or fluoride of a metal or a mixture thereof.

22. The high-density read-only optical disc of claim 18, wherein the dielectric material is ZnS-SiO₂。

23. The high-density read-only optical disc of claim 18, further comprising a dielectric layer on at least one surface of the mask layer, the dielectric layer comprising a metal oxide, nitride, sulfide, or fluoride, or a mixture thereof.

24. The high-density read-only optical disc of claim 23, wherein the dielectric layer is formed of ZnS-SiO₂And (4) forming.

25. The high-density read-only optical disc of claim 18, further comprising Sb or Sb between the substrate and the mask layer₂Te₃A crystalline read assist layer of composition.

26. The high-density read-only optical disc of claim 18, further comprising a reflective layer on the mask layer.

27. The high-density read-only optical disc of claim 26, wherein the reflective layer comprises a metal selected from the group consisting of Au, Al, Cu, Cr, Ag, Ti, Pd, Ni, Zn, Mg, and alloys thereof.

28. The high-density read-only optical disc of claim 26, wherein the reflective layer is formed to have a thickness of 50-150 nm.

29. The high-density read-only optical disc of claim 28, wherein the reflective layer is formed to have a thickness of 60-120 nm.

30. A high-density read-only optical disc that allows reading of marks having a size not larger than a reading resolution limit of a laser beam, the disc comprising:

a super-resolution near-field structure having a substrate and a mask layer, wherein the substrate has a plurality of pits that differ in length according to unit information, wherein a depth of a pit of the plurality of pits increases as a pit length of the pit increases.

31. The high-density read-only optical disc of claim 30, wherein a depth of a pit of the plurality of pits increases as a pit length of the pit increases; the mask layer contains a metal oxide or a mixture of fine metal particles and a dielectric material.