WO2006134528A2

WO2006134528A2 - Optical recording medium and method of manufacturing an optical recording medium

Info

Publication number: WO2006134528A2
Application number: PCT/IB2006/051840
Authority: WO
Inventors: Marius I. Boamfa; Jacobus H. M. Neijzen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-06-14
Filing date: 2006-06-09
Publication date: 2006-12-21
Also published as: WO2006134528A3; TW200735084A

Abstract

The present invention relates to an optical recording medium (10) having a layer (12), the optical properties of which are changed upon projecting a light beam with a given spot (20) size onto a surface (14) of the layer for writing data onto the optical recording medium, wherein the surface comprises regions (16) of a first type and regions (18) of a second type, the optical-properties changing-behavior of the regions of the first type and of the regions of the second type are different, and the width of the regions of the second type perpendicular to a writing direction is smaller than the spot size. The present invention further relates to a method of manufacturing an optical recording medium.

Description

Optical recording medium and method of manufacturing an optical recording medium

FIELD OF THE INVENTION

The present invention relates to an optical recording medium and to a method of manufacturing an optical recording medium. Particularly, the present invention relates to optical recording with high data densities.

BACKGROUND OF THE INVENTION

In optical recording and optical mastering (for general information see: A.B. Marchant, "Optical Recording - A technical Overview", Addison-Wesley, 1990) the ultimate resolution (data density) is related to the optical spot size of the writing beam. For a given system the optical spot size is directly proportional to the light wavelength and inverse proportional to the numerical aperture (NA) of the focusing lens.

Figure 1 shows a diagram illustrating a common definition of the optical spot size. The light intensity, normalized to 1.0, of a laser beam projected onto a surface is illustrated in dependence on the reduced length (λ/NA). The optical spot size can be defined as the reduced length at a light intensity of 0.5, i.e. approximately 0.62 λ/NA.

In consumer optical recording devices the light source choice is limited to lasers that can be fabricated in a very compact design. At present 405 nm is the shortest wavelength diode laser. By the same compact design and price limitations the lens NA is limited to about 0.85 (for far- field). These numbers corresponds to an optical spot size of about 300 nm. This optical spot size is sufficient for the Blu-Ray generation of optical storage both for the Recordable and Rewritable (R/RW) options. However, for data densities beyond the Blu-Ray, as for example Two Dimensional Optical Storage (TwoDOS, see A. van der Lee, D. Bruls, C. Busch, A. Immink, W. Coene and A. Hekstra: Jpn. J. Appl. Phys. 43 (2004), 4912) the present spot size does not allow the R and RW options. An attempt to further decrease the optical spot size would only add complexity and render the compact design required for a consumer device as impossible.

A similar situation is encountered in Near Field optical storage. With a laser wavelength of 405 nm and a NA of 1.6 - 1.7, the optical spot size is about 150 nm. This size is sufficient to read ROM media mastered by another method but is a serious impediment for R and RW options at the data densities the Near Field project is aiming at.

In optical mastering the light source choice is imposed by the lowest continuous mode laser, at present 257 nm. A typical NA is between 0.9 for far field mastering to about 1.2 in Liquid Immersion Mastering (J.H.M. Neijzen, E.R. Meinders and H. van Santen, "Liquid Immersion Deep-UV Optical Disc Mastering for Blu-ray Disc Read- OnIy Memory", Jpn. J. Appl. Phys. 43, p. 5047, 2004). With an optical spot size of 130 nm the maximum data densities able to be mastered lies below the requirement of a fourth generation optical storage standard. These hard boundaries are in direct contradiction with the general trend in data densities increase for optical storage.

Thus, a novel concept is desired that allows optical recording and optical mastering beyond the limit of the optical spot size imposed by the light wavelength and NA.

It is therefore an object of the invention to provide a novel concept for optical data mastering and optical data recording at data densities beyond the limit imposed by the optical spot size.

SUMMARY OF THE INVENTION

The above objects are solved by the features of the independent claims. Further developments and preferred embodiments of the invention are outlined in the dependent claims.

In accordance with the invention, there is provided an optical recording medium having a layer, the optical properties of which are changed upon projecting a light beam with a given spot size onto a surface of the layer for writing data onto the optical recording medium, wherein the surface comprises regions of a first type and regions of a second type, the optical-properties changing-behavior of the regions of the first type and of the regions of the second type are different, and the width of the regions of the second type perpendicular to a writing direction is smaller than the spot size. Generally, an optical recording medium is dedicated for the use of a particular optical spot size, various optical spot sizes or a range or ranges of optical spot sizes. Therefore, the optical spot size is usable in terms of defining the structural properties of the optical recording medium. According to the present invention the optical recording medium has different regions that behave differently upon light exposure. The regions of the second type are smaller than the optical spot size. Therefore, the optical spot projected onto the surface is partly projected onto a region of the first type and partly onto the region of the second type. A characteristic change of the optical appearance of the second type region is therefore smaller than the optical spot.

Particularly, the regions of the second type change their optical properties upon projecting a light beam onto the surface of the layer and the regions of the first type do not change their optical properties upon projecting a light beam onto the surface of the layer. In other words, the surface of the optical recording medium is subdivided into optical active and optical passive regions. Only the optical active medium shows a change upon illumination, so that a written mark on the surface is restricted to the active region and surrounded by a non-changed area on the passive region. According to a preferred aspect of the present invention, the regions of the first type and the second type form spiral stripes alternating in a radial direction, and the widths of the regions of the first type and the second type are substantially equal, thereby obtaining a track pitch that is substantially twice the width of the regions. Thus, an alternation of active and passive media stripes is provided. In this way, the radial data density is increased up to a factor of 3, while along the track the data density remains constant. Since, as described in further detail below, the primary structure is the result of a replication process, the symbol length in writing direction has to be considered. Generally, longer symbols are easier replicated. Therefore, the symbol length can be slightly increased without a negative influence on the basic features of the present invention. According to a particular embodiment of the present invention, the width of the regions is between 90 and 110 nm, and the track pitch is between 180 and 220 nm. With the help of a Laser Beam Recording (LBR) mastering facility or a Liquid Immersion Mastering (LIM) facility a master can be produced having a grooved structure with a width of for example 100 nm and with a track pitch of 200 nm. In the same mastering process, synchronization marks can be added as a wobble of the groove structure. This is particularly relevant for TwoDOS because TwoDOS requires that the optical data are track-to-track synchronized. Generally, a consumer-end device does not have the stability of a mastering machine, and therefore it has to use synchronization marks for the data synchronization. One way to implement such synchronization marks is the mentioned addition of a periodic wobble in the groove structure. The present embodiment is an example of the realization of a TwoDOS R/RW disc on the basis of LBR mastering or Liquid Immersion Mastering.

According to a different embodiment, the width of the regions is between 30 and 50 nm, and the track pitch is between 60 and 100 nm. With the help of an Electron Beam Recorder mastering facility a master can be made such that the width of the groove corresponds to one third of the optical spot of a Deep-UV LBR mastering machine (257 nm, NA=0.9).

According to a further preferred embodiment of the present invention, the width of the regions is between 50 and 90 nm, and the track pitch is between 100 and 180 nm. Thus, Near Field R/RW can be supported by an Electron Beam Recorder mastering facility, since by such means a master can be made such that the width of the grooves corresponds to one third of the optical spot of the Near Field device.

It is also possible that the width of the regions is between 120 and 200 nm, and the track pitch is between 240 and 400 nm. Thus, the optical storage medium can be mastered with the help of a relatively inexpensive technology based on the existent laser diode with a wavelength of 405 nm, or some other wavelengths nearby. The spot size of a 405 nm laser focused with a 0.85 NA lens is about 295 nm in diameter.

Various materials can be chosen for the passive medium. For example, it can be preferred that the regions of the second type are formed from a photo-sensitive resist. Similarly it is possible that the regions of the second type are formed from a phase-change medium.

According to a still further embodiment the regions of the second type are formed from a photo-thermal sensitive medium.

According to one of the applications of the present invention the optical recording medium is a recordable or rewritable disc.

It is also possible that the optical recording medium is the basis for a stamper used for the mass production of optical discs.

In accordance with a further aspect of the present invention, there is provided a method of manufacturing an optical recording medium for writing data onto the recording medium by projecting a light beam with a given spot size onto a surface of a layer of the recording medium, the method comprising the steps of: providing a substrate having a grooved surface made from a first material having a first optical-properties changing-behavior upon projecting a light beam onto the material, the width of the grooves perpendicular to a writing direction being smaller than the spot size, depositing a second material onto the grooved surface of the substrate, the second material having a second optical-properties changing-behavior different from the first optical-properties changing-behavior upon projecting a light beam onto the material, and removing a part of the deposited second material such that a surface with regions of a first type and regions of a second type is obtained.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a diagram illustrating a common definition of the optical spot size.

Figure 2 shows a top view and a cross sectional view of a section of an optical recording medium according to the present invention;

Figure 3 shows a top view of a section of an optical recording medium according to the present invention after illumination;

Figure 4 shows an illustration of process steps for realizing a method of manufacturing an optical recording medium according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 2 shows a top view (a) and a cross sectional view (b) of a section of an optical recording medium according to the present invention. The optical recording medium 10 comprises a layer 12 having a patterned surface 14. The patterning is realized by an alternation of regions 16, 18 that have different optical properties. Particularly, the optical- properties changing-behavior of the regions 16, 18 is different due to a different choice of materials 28, 30 for the different regions 16, 18.

Figure 3 shows a top view of a section of an optical recording medium according to the present invention after illumination. When an optical spot 20 for recording data on the optical recording medium 10 is projected onto the optical recording medium 10, data marks 32 are generated. According to a preferred embodiment, the regions 18 change their optical properties upon illumination, while the optical regions 16 do not change their optical properties. Thus, the data marks are generated only in the regions 18, i.e. in the active exposed medium. It is also possible, that both of the regions change their optical properties upon projecting a light beam onto the surface; however, according to the present invention, the optical properties changing behavior of the region 16, 18 has to be different. From the illustration it can be seen that the radial data density, i.e. the density perpendicular to the extension of the stripes, is increased up to a factor of 3. This concept allows an increase in data density without iurther increasing the optics complexity. The concept allows a direct control over the written symbol width, removing the need of a complex write strategy.

Figure 4 shows an illustration of process steps for realizing a method of manufacturing an optical recording medium according to the present invention. The steps (a) , (b) and (c) show subsequent method steps. In a first step (a) substrate 22 is mastered with a high resolution device, for example by means of Laser Beam Recording (LBR) mastering, Liquid Immersion Mastering (LIM) or Electron Beam Recording (EBR) mastering. The substrate 22 is made from a first material 28 that has a particular optical-properties changing- behavior. Preferably, the first material 28 is optically passive. A grooved surface is formed on the substrate 22, the grooves 26 having a width that is smaller than the optical spot to be applied for writing data on the finalized optical recording medium. The structure is replicated in a passive medium, for example by injection molding or by a photo-polymerization process.

In a step (b) a second material 30 is deposited on the first material 28. The second material 30 has an optical-properties changing-behavior different from the first material 28. Particularly, the second material 30 is active, in contrast to the passive first material 28. The deposition step (b) is performed for example by spin coating or sputtering.

In a further step (c) the excess of active medium 30 is removed via an etching step, such that the patterned surface 14 of the optical recording medium remains.

In the field of mastering the present invention opens the way to higher data densities for all type of Laser Beam Recording (LBR) mastering devices. In the field of optical recording this invention makes available the option of Recordable/Re Writable (R/RW) for formats like TwoDOS and Near Field.

Equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS:

1. An optical recording medium (10) having a layer (12), the optical properties of which are changed upon projecting a light beam with a given spot (20) size onto a surface (14) of the layer for writing data onto the optical recording medium, wherein the surface comprises regions (16) of a first type and regions (18) of a second type, the optical-properties changing-behavior of the regions of the first type and of the regions of the second type are different, and the width of the regions of the second type perpendicular to a writing direction is smaller than the spot size.

2. An optical recording medium (10) according to claim 1, wherein the regions (16) of the second type change their optical properties upon projecting a light beam onto the surface (14) of the layer (12) and the regions (18) of the first type do not change their optical properties upon projecting a light beam onto the surface of the layer.

3. An optical recording medium (10) according to claim 1, wherein the regions (16, 18) of the first type and the second type form spiral stripes alternating in a radial direction, and the widths of the regions of the first type and the second type are substantially equal, thereby obtaining a track pitch that is substantially twice the width of the regions.

4. An optical recording medium (10) according to claim 3, wherein the width of the regions (16, 18) is between 90 and 110 nm, and the track pitch is between 180 and 220 nm.

5. An optical recording medium (10) according to claim 3, wherein the width of the regions (16, 18) is between 30 and 50 nm, and the track pitch is between 60 and 100 nm.

6. An optical recording medium (10) according to claim 3, wherein the width of the regions (16, 18) is between 50 and 90 nm, and the track pitch is between 100 and 180 nm.

7. An optical recording medium (10) according to claim 3, wherein the width of the regions (16, 18) is between 120 and 200 nm, and the track pitch is between 240 and 400 nm.

8. An optical recording medium (10) according to claim 1, wherein the regions

(18) of the second type are formed from a photo-sensitive resist.

9. An optical recording medium (10) according to claim 1, wherein the regions (18) of the second type are formed from a phase-change medium.

10. An optical recording medium (10) according to claim 1, wherein the regions (18) of the second type are formed from a photo-thermal sensitive medium.

11. An optical recording medium (10) according to claim 1, wherein the optical recording medium (10) is a recordable or rewritable disc.

12. An optical recording medium (10) according to claim 1, wherein the optical recording medium (10) is the basis for a stamper used for the mass production of optical discs.

13. A method of manufacturing an optical recording medium (10) for writing data onto the recording medium by projecting a light beam with a given spot (20) size onto a surface (14) of a layer (12) of the recording medium, the method comprising the steps of: providing a substrate (22) having a grooved surface (24) made from a first material (28) having a first optical-properties changing-behavior upon projecting a light beam onto the material, the width of the grooves (26) perpendicular to a writing direction being smaller than the spot size, depositing a second material (30) onto the grooved surface of the substrate, the second material having a second optical-properties changing-behavior different from the first optical-properties changing-behavior upon projecting a light beam onto the material, and removing a part of the deposited second material such that a surface with regions of a first type and regions of a second type is obtained.