JP2005174425A - Optical recording medium, reproducing method of optical recording medium, and manufacturing method of optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical recording medium for recording information with unevenness, which is densified without reducing throughput, and which can be used for authoring at low cost. Another object of the present invention is to provide a method for reproducing information using the optical recording medium.
An optical recording medium of the present invention is an optical recording medium that records and reproduces information by light, and includes at least a thin-film light absorbing layer that absorbs reproduced light and generates heat, and a convex shape that is in contact with the light absorbing layer. The structure is laminated on the support.
[Selection] Figure 1

Description

  The present invention relates to an optical recording medium for recording / reproducing information by laser light, a method for reproducing the optical recording medium, and a method for producing the optical recording medium.

  In recent years, read-only media (ROM disks) have become widespread, especially DVD-ROMs. Development of high-density ROM disks using blue lasers is also urgent.

The ROM disk records information by using a relief pattern of irregularities, and is manufactured through complicated processes such as master production, stamper creation, and replication.
In the master production process, a master is produced by the procedures of photoresist exposure by laser beam or electron beam irradiation, pattern formation by resist development, and substrate etching using a resist as a mask. In the stamper described above, the stamper is created by nickel (Ni) plating and Ni peeling procedures on the master. In the replication step, a predetermined concavo-convex pattern is transferred to the resin material using the stamper as a mold.

  Further, in the ROM disk manufacturing process, test recording is performed in order to confirm and adjust recording conditions, compression efficiency, coding, authoring, and the like. For this trial recording, the use of a ROM disk manufactured through all the processes is limited in terms of cost. Therefore, in order to easily confirm authoring and the like, a recording medium having a recording layer of a phase change material or an organic dye is used as a test recording medium (hereinafter referred to as an authoring medium). For example, the authoring media include those disclosed in Patent Document 3 and Patent Document 4.

  However, a conventional medium for recording information using a relief pattern of unevenness has a problem that fine unevenness transfer becomes difficult due to higher density. In order to solve this problem, higher density by electron beam drawing has been studied. For example, a patent document discloses a mastering technique by electron beam drawing (Patent Document 1 and Patent Document 2). However, the high density by the conventional electron beam drawing has a problem that the throughput is lowered and a manufacturing cost is increased. There is also a problem that there is no authoring recording medium that can record and reproduce at the same density.

JP 2001-344833 A JP 2003-051437 A Japanese Patent Laid-Open No. 11-328738 JP 2001-126255 A JP 2003-168249 A

  SUMMARY OF THE INVENTION In view of the above-described conventional problems, the present invention provides an inexpensive optical recording medium for recording information with unevenness, which is densified without reducing throughput, and can be used for authoring at low cost. With the goal. Another object of the present invention is to provide a method for reproducing information using the optical recording medium.

According to the present invention, the following optical recording medium, optical recording medium reproducing method, and optical recording medium manufacturing method are provided.
[1] In an optical recording medium for recording and reproducing information by light, at least a thin-film light absorption layer that absorbs reproduction light and generates heat, and a convex shape that is in contact with the light absorption layer and is made of a different material from the light absorption layer An optical recording medium, wherein the structure is laminated on a support.
[2] Using the optical recording medium described in [1] above, a laminated body composed of a thin-film light absorption layer and a convex structure is irradiated with light from the convex structure side, and reflected. A method for reproducing an optical recording medium, comprising detecting a change in light quantity.
[3] In an optical recording medium that records and reproduces information by light, at least a thin-film light absorption layer that absorbs reproduction light and generates heat, a convex structure in contact with the light absorption layer, and reproduction light An optical recording medium, wherein a light transmitting layer having transparency is laminated, and the light transmitting layer is laminated in a hemispherical shape following the convex structure.
[4] Using the optical recording medium according to the above [3], light is irradiated from the light transmitting layer side to a laminated body composed of a thin light absorbing layer, a convex structure, and a light transmitting layer. And a method of reproducing an optical recording medium, wherein a change in the amount of reflected light is detected.
[5] The optical recording medium according to [1] or [3], wherein the convex structure has a cylindrical shape, and a diameter of the convex structure changes according to recording information.
[6] Using the optical recording medium described in [5] above, light is irradiated to a convex structure whose diameter changes according to recorded information, and reflected according to the period of the convex structure. A method for reproducing an optical recording medium, comprising detecting a change in light quantity.
[7] The above [1] or [1], wherein the convex structure has a cylindrical shape, and the arrangement of the convex structures in the surface of the optical recording medium is a closely packed arrangement (three-fold symmetry arrangement). [3] The optical recording medium according to [3].
[8] Using the optical recording medium described in [7] above, the convex structure is irradiated with light to simultaneously reproduce a plurality of track rows, and the amount of reflected light corresponding to the period of the convex structure is A method of reproducing an optical recording medium, characterized by detecting a change.
[9] The optical recording medium according to [7], wherein the optical recording medium is a convex structure provided with rows in which no convex structure exists every n rows in the radial direction of the optical recording medium.
[10] A method for reproducing an optical recording medium, wherein the optical recording medium according to [9] is used to simultaneously reproduce n−1 rows and detect the amount of reflected light.
[11] The above [1] [3] [5] [7] [7], wherein the light absorption layer material contains at least one element selected from Sb, Te, In, Bi, and Ga. 9] The optical recording medium according to any one of [9].
[12] The thin film material constituting the convex structure contains ZnS and SiO _2. Any one of [1] [3] [5] [7] [9] [11] The optical recording medium described.
[13] A lamination step of laminating at least a thin film-shaped light absorption layer and a thin film material for forming a convex structure on a support substrate to form a laminate, and the convex structure from the convex structure side. [1] [3] [5] [7] [9] including at least a recording step of recording information by irradiating light and a removing step of removing a non-recorded portion to form a convex structure [11] The method for producing an optical recording medium according to any one of [12].

With the medium configuration according to the first aspect of the present invention and the reproduction method according to the third aspect, super-resolution reproduction is possible, and a period less than the diffraction limit can be reproduced. It is possible to increase the density of a medium on which information is recorded with unevenness.
With the medium configuration according to the third aspect of the present invention and the reproduction method according to the fourth aspect, it is possible to collect light on the medium and to perform super-resolution reproduction, and it is possible to reproduce a period below the diffraction limit. It is possible to increase the density of a medium on which information is recorded with a convex structure.
The medium configuration according to the fifth aspect of the present invention and the reproducing method according to the sixth aspect make it possible to multi-value the recorded information corresponding to the diameter of the convex structure, and to increase the density of the medium on which information is recorded with unevenness. Can be planned.
With the medium configuration according to the seventh aspect of the present invention and the reproducing method according to the ninth and tenth aspects, a plurality of convex structures can be reproduced simultaneously, and the density can be increased by reducing the track pitch.
With the light absorption layer material according to claim 11 of the present invention, a high-density convex structure can be reproduced by super-resolution reproduction.
With the light absorption layer material according to claim 12 of the present invention, a high-density convex structure can be formed in a large area without a mask.
With the medium manufacturing method according to the thirteenth aspect of the present invention, a high-density convex structure can be formed in a large area without a mask.

Hereinafter, the present invention will be described in more detail.
The optical recording medium of the present invention is a recording medium for recording and reproducing information by light. The optical recording medium of the present invention has the following five types of modes, and five types of recording and reproduction are corresponding to each of the modes. There is a way. The first to fifth optical recording media and the first to fifth recording / reproducing methods will be described in the following order.

The first optical recording medium in the present invention aims to increase the recording density by super-resolution reproduction. In the medium, at least a thin-film light absorption layer that absorbs reproduction light and generates heat, and a convex structure in contact with the light absorption layer are laminated on a support.
FIG. 1A shows an example of the configuration of the first optical recording medium. In the optical recording medium shown in FIG. 1A, a thin film buffer layer 102 that protects a support substrate is laminated on a support substrate 101, and the thin film light absorption layer 103 and the light absorption layer are in contact therewith. Convex structures 104 are stacked. Each of the convex structures 104 is separated in the medium plane as illustrated.

  As the material of the support substrate 101, it is preferable to use polycarbonate, acrylic resin, polyolefin, epoxy, vinyl ester, ultraviolet curable resin, glass, quartz, or the like. Pregrooves and prepits for tracking laser light may be provided on the surface of the support substrate 101.

The thin-film buffer layer 102 is preferably SiO ₂ or a mixture of SiO ₂ and a compound such as ZnS, ZnO, SiN, Al ₂ O ₂ , and AlN.

  As the thin-film light absorption layer 103, a compound containing a low melting point metal material is preferably used. The low melting point metal material preferably contains at least one element selected from Sb, Te, In, Bi, and Ga. Specifically, binary materials such as SbTe, InTe, BiTe, and GaSb, ternary materials such as GeSbTe, InSbTe, BiSbTe, and GaSbTe, and quaternary materials such as AgInSbTe are used. Further, a semiconductor material such as Si, Ge, GaAs, or InP can also be used.

These materials constituting the light absorption layer 103 generate heat due to irradiation with a relatively low power laser beam, and the phase state changes. The optical characteristics such as the refractive index and the absorption coefficient change due to the change of the phase state. By laminating these materials with the convex structure, the optical characteristics of the region corresponding to the convex structure can be changed by low-power laser light irradiation.
Further, since the material is in an amorphous state, the residual stress in the thin film is reduced. Therefore, in the method for manufacturing the optical recording medium of the present invention (the manufacturing method will be described later), a steep temperature change occurs. In spite of the occurrence, defects such as cracks can be suppressed. With this effect, a fine convex structure can be formed over a large area.

As the convex structure 104, a ZnS—SiO ₂ mixture is preferably used. Insulator materials such as SiO ₂ , ZnS, ZnO, SiN, Al ₂ O ₂ , and AlN can be used alone. A protective layer may be provided on the convex structure 104. As the protective layer, a silicon compound such as SiN, SiO ₂ or SiC, or a permeable resin can be used.

In the first reproducing method of the present invention, the first optical recording medium is used, and the convex structure 104 is formed with respect to the laminate composed of the thin light absorption layer 103 and the convex structure 104. Light is irradiated from the side, and a change in the amount of reflected light is detected. FIG. 1B shows an example of the first reproduction method.
In the first reproduction method, laser light is incident from the convex structure 104 side as shown in FIG. In FIG. 1B, 201 indicates the incident direction of laser light.
The incident laser light is absorbed by the light absorption layer 103 and the light absorption layer 103 generates heat. Since the light-absorbing layer and the convex structure are different materials, the amount of heat generated changes directly under the convex structure. With the change in the heat generation amount, the optical characteristics of the light absorption layer change at the timing of the convex structure. Corresponding to the change in the optical characteristics, the reproduction signal changes at the timing of the convex structure.

FIG. 1C shows a laser intensity distribution 204 of incident laser light and a temperature distribution 205 on the surface of the optical recording medium. As shown in FIG. 1C, the laser light intensity distribution 204 is a Gaussian distribution. In FIG. 1C, reference numeral 202 denotes an optical property changing region in the light absorption layer.
When the convex structure 104 is provided on the medium surface, the temperature distribution is in a state corresponding to the convex structure 104, and the vicinity of the convex structure 104 located near the center of the beam becomes particularly high. As a result, the optical characteristics immediately below the convex structure 104 located near the beam center change. By changing the optical characteristics of the region smaller than the beam diameter corresponding to the convex structure 104, the reproduction signal changes at the timing of the convex structure 104 even in the period below the diffraction limit. High density is achieved by such super-resolution reproduction.
Reference numeral 206 denotes a temperature threshold at which the optical characteristics of the light absorption layer change greatly.

The second optical recording medium in the present invention is intended to increase the recording density by super-resolution reproduction and the condensing effect of the laser beam on the medium. In this medium, at least a thin-film light absorption layer that absorbs reproduction light and generates heat, a convex structure that is in contact with the light absorption layer, and a light transmission layer that is transparent to the reproduction light are laminated. The light transmission layer is laminated in a hemispherical shape following the convex structure.
FIG. 2A shows an example of the configuration of the second optical recording medium. In the optical recording medium shown in FIG. 2A, a thin film buffer layer 302 that protects the support substrate is laminated on the support substrate 301, and a thin film light absorption layer 303 and a light absorption layer are formed on the buffer layer 302. A convex structure 304 in contact with the light transmission layer 305 is stacked, and the light transmission layer 305 has a vertical cross-sectional shape stacked in a semicircular shape following the convex structure 304. Each of the convex structures 304 is separated in the medium plane as illustrated.

  The support substrate 301 is configured in the same manner as the support substrate 101 of the first optical recording medium, and the thin-film buffer layer 302 is configured in the same manner as the buffer layer 102 of the first optical recording medium. The absorption layer 303 is configured in the same manner as the light absorption layer 103 of the first optical recording medium.

As the light transmission layer 305, an oxide, a nitride, or a fluorine compound having high transmittance with respect to reproduction light can be used. The oxide is preferably SiO ₂ , Al ₂ O ₃ , BiAlO ₃ , BiGeO, La ₂ O ₃ , LaAO _3, etc., the nitride is preferably SiN, AlN, etc., and the fluorine compound is CaF ₂ , A material such as BaF ₂ is preferred.

In the second reproducing method of the present invention, the second optical recording medium is used, and a light-emitting layer 303, a convex structure 304, and a light transmission layer 305 are laminated on the laminated body. Light is irradiated from the transmissive layer 305 side to detect a change in the amount of reflected light. FIG. 2B shows an example of the second reproduction method.
In the second reproduction method, laser light is incident from the convex structure 304 side as shown in FIG. In FIG. 2B, 401 indicates the incident direction of laser light.

  In the second reproducing method of the present invention, the incident laser light is absorbed by the light absorption layer 303 and the light absorption layer 303 generates heat. The light transmission layer 305 in the second optical recording medium is laminated so that its longitudinal cross-sectional shape becomes a semicircular shape following the convex structure 304, so that a part of the laser beam is shown in the figure. Is further collected at the medium surface. The condensed laser light is absorbed by the light absorbing layer 303, and the light absorbing layer near the convex structure 403 located at the center of the beam generates heat. Optical characteristics such as refractive index and absorption coefficient change due to heat generation. Note that reference numeral 402 denotes a change region of optical characteristics in the light absorption layer.

  Since the second optical recording medium is provided with the light-transmitting layer 305 having a semicircular longitudinal cross section, the light condensing effect is increased, and the convex shape is the same as the reproducing method of the first optical recording medium. Due to the super-resolution reproduction effect due to the change in optical characteristics in a region smaller than the beam diameter corresponding to the structure 304, the signal intensity from the convex structure 304 having a period equal to or less than the diffraction limit increases. As a result, excellent super-resolution reproduction is possible due to the condensing effect of the laser beam on the optical recording medium, and high recording density is achieved.

The third optical recording medium in the present invention is intended to increase the recording density by multi-value recording in addition to the purposes of the first and second optical recording media. In the medium, in addition to the configuration of the first and second optical recording media, the convex structure is cylindrical, and the diameter of the convex structure changes depending on the recording information. Yes.
FIG. 3 shows an example of a top view of the configuration of the third optical recording medium. 3, reference numeral 501 denotes a light absorbing layer, 502 denotes a convex structure, 503 denotes a period of the convex structure in the track direction, 504 denotes a recording track, and 505 denotes the diameter of the convex structure.
The laminated structure and the material of each layer in the third optical recording medium are the same as those in the first and second optical recording media. The convex structure 502 in the third optical recording medium has a cylindrical shape. The period of the convex structure 502 in the track direction is constant. The diameter 505 of the convex structure changes depending on the recorded information.

  In the third reproducing method of the present invention, the above-mentioned third optical recording medium is used to irradiate light onto the convex structure 502 whose diameter changes according to the recorded information, and A change in the amount of reflected light is detected corresponding to the period. FIG. 4 shows an example of the third reproduction method. 4A is a diagram showing a top view of the optical recording medium, and FIG. 4B is a diagram showing a change in signal level. 6A, reference numeral 601 denotes a laser beam, 502 denotes a convex structure, 503 denotes a period of the convex structure, and 504 denotes a track. 4B, reference numeral 611 denotes a reproduction signal level sampled at the timing A, and reference numeral 612 denotes a reproduction signal level sampled at the timing H.

  In the third reproduction method, multi-value information is recorded in correspondence with a change in the diameter of the convex structure. When the laser beam is located at the center of the convex structure 502, the amount of reflected light changes according to the diameter. As shown in the figure, by detecting (sampling) the signal level at the period 503 of the convex structure, multivalue information corresponding to the change in diameter can be determined as the change in signal level. As a result, an improvement in recording density is achieved.

The fourth optical recording medium in the present invention aims to increase the recording density by narrowing the track pitch in addition to the purpose of the first and second optical recording media. In the medium, in addition to the configurations of the first and second optical recording media, the convex structure is cylindrical, and the arrangement of the convex structures in the surface of the optical recording medium is a closely packed arrangement (three Symmetric arrangement).
FIG. 5 shows an example of a top view of the configuration of the fourth optical recording medium. In FIG. 4, reference numeral 701 denotes a light absorbing layer, 702 denotes a convex structure, 703 denotes a period of the convex structure in the track direction, and 704 denotes a virtual lattice point of a closely packed arrangement (three-fold symmetry arrangement). .

  The laminated structure and the material of each layer in the fourth optical recording medium are the same as those in the first and second optical recording media. The convex structure 702 in the fourth optical recording medium has a cylindrical shape and a constant diameter. The arrangement of the convex structures 702 in the medium plane is a closely packed arrangement (three-fold symmetry arrangement). Depending on the recorded information, there are lattice points where there are convex structures 702 and lattice points where there are no convex structures 702.

In the fourth reproducing method of the present invention, the fourth optical recording medium is used to irradiate the convex structure 702 with light to reproduce a plurality of tracks at the same time, corresponding to the period of the convex structure 702. Thus, a change in the amount of reflected light is detected.
FIG. 6 shows an example of the fourth reproduction method. FIG. 6A is a top view of the optical recording medium. In FIG. 6A, reference numeral 702 denotes a convex structure, 703 denotes a period of the convex structure, and 801 denotes laser light. FIG. 6 shows a convex structure for three tracks.

In the fourth reproduction method of the present invention, a row of convex structures 702 having a plurality of tracks (at least two tracks or more) is reproduced simultaneously. Here, the simultaneous reproduction means that a plurality of convex structure rows are included in the beam diameter.
Preferably, as shown in FIG. 6B, three rows of convex structure rows are simultaneously reproduced in the radial direction. In the track direction, the reproduction signal is detected (sampled) at timings A, B, C, D... Of the convex structure period 703.

  FIG. 6B is a diagram showing changes in the reproduction signal level. In FIG. 6A, reference numeral 811 denotes a reproduction signal level sampled at the timing A, and reference numeral 812 denotes a signal level sampled at the timing D. The number of structures included in the laser beam diameter 801 changes at 7 timings, 6 at B, 5 at C, and 5 at D. As a result, the amount of reflected light changes. When the signal is sampled at the timing of the period 703 of the convex structure, the beams are overlapped in the track direction, and one convex structure is detected a plurality of times. By detecting a plurality of times, it is possible to determine recording information corresponding to the arrangement and presence / absence of a structure using a signal processing technique (PRML). As described above, by increasing the arrangement of the convex structures in the medium plane into a finely packed arrangement (three-fold symmetric arrangement) and simultaneously reproducing a plurality of structures, a high density can be achieved by narrowing the track pitch. .

The fifth optical recording medium according to the present invention is intended to reproduce a plurality of tracks simultaneously with high accuracy in addition to the purpose of the fourth optical recording medium in which the track pitch is narrowed. In addition to the configuration of the fourth optical recording medium, the medium is provided with a row in which no convex structure exists in every n rows in the radial direction of the optical recording medium.
FIG. 7 shows an example of a longitudinal sectional view of the fifth optical recording medium in the radial direction of the optical recording medium. In FIG. 7, reference numeral 901 denotes a support substrate, 902 denotes a buffer layer, 903 denotes a light absorption layer, 904 denotes a convex structure, 905 denotes a light transmission layer, and 906 denotes a track pitch.

  The arrangement of the convex structures 904 in the plane of the fifth optical recording medium is a closely packed arrangement (three-fold symmetry arrangement). In the radial direction of the optical recording medium, every n rows are provided with a row where no convex structure 904 is present. Preferably, every fourth row is provided with a row where the convex structures 904 are not present. In the tracks a, b, c, d, and e shown in FIG. 6, the convex structures 904 do not exist in the tracks a and e. Accordingly, the convex structures 904 can be densely and densely within the plane of the optical recording medium. As a result, when the light transmission layer 905 is laminated, the portions b, c, d where the convex structures are dense are filled with the film, and grooves are formed in the rough portions a, e. With this configuration, since a tracking step can be formed at a predetermined position, high density can be achieved by narrowing the track pitch by simultaneously reproducing a plurality of convex structures 904.

In the fifth reproducing method of the present invention, the fifth optical recording medium is used to simultaneously reproduce the n-1 column and detect the amount of reflected light.
FIG. 8 shows an example of the fifth reproduction method. FIG. 8A is a top view of the optical recording medium, and FIG. 8B is a longitudinal sectional view in the radial direction of the optical recording medium. In FIG. 8, reference numeral 904 denotes a convex structure, 906 denotes a track pitch, and 1001 denotes laser light.

In the fifth reproducing method of the present invention, the convex structures 904 are not present on the tracks a and e. As a tracking method, a push-pull method or a differential push-pull method is used. The diffracted light and reflected light from the groove portions a and e are detected by a photodiode divided into two along the track direction, and a push-pull signal is generated. The push-pull signal is used as a tracking servo error signal.
In the method of the present invention, the push-pull signal is generated from the diffracted light and the reflected light from the convex structure rows a and e, thereby tracking the laser light with respect to the convex structure rows b, c, and d. Can be played at the same time. By simultaneously reproducing a plurality of structures, high density can be achieved by narrowing the track pitch.

A method for producing an optical recording medium of the present invention includes a laminating step of laminating at least a thin-film light absorption layer and a thin film material that forms a convex structure on a support substrate, Thus, it includes at least a recording step of recording information by irradiating light from the convex structure side, and a removal step of forming a convex structure by removing an unrecorded portion.
An example of the manufacturing method of the present invention is shown in FIG. FIG. 9A shows a stacking process of each layer, FIG. 9B shows an information recording process, and FIG. 9D shows an unrecorded part removing process.
In FIG. 9A, reference numeral 1101 denotes a support substrate, 1102 denotes a buffer layer, 1103 denotes a light absorption layer, and 1104 denotes a thin film forming a convex structure.

In FIG. 9B, 1111 indicates the irradiation direction of the laser beam. Laser light is irradiated from the thin film 1104 side that forms the convex structure.
Reference numeral 1112 denotes a modified portion by laser light irradiation. The material density, crystal state, composition, and the like of the thin film change due to heat generation of the light absorption layer.
FIG. 9C shows a laser light irradiation method. P1 and P2 indicate laser power levels. The power level is changed by 2 levels. The laser power level is set to a relationship of P1> P2, and the period S and the period T1 held at the P1 level are changed according to the recording information.

In FIG. 9D, reference numeral 1121 denotes a convex structure. Processing is performed by solution etching. As an etching solution, it is preferable to use an aqueous solution containing hydrofluoric acid (hydrofluoric acid). The optical recording medium is immersed in a hydrofluoric acid solution to remove unrecorded parts. Etching using such a solution increases the etching rate ratio (selection ratio) between recorded and unrecorded recording materials having different material densities, crystal states, compositions, and the like.
Further, since the material of the base light absorption layer 1103 and the layer forming the convex structure body 1121 are different, the selection ratio with the base can be increased. In a large area device such as an optical recording medium, a convex structure can be formed with good in-plane uniformity. According to the method of the present invention, a fine convex structure having a large area can be formed by a maskless process without using photolithography.

As described above, the thin film material constituting the convex structure in the optical recording medium of the present invention preferably contains ZnS and SiO ₂ . Such a ZnS—SiO ₂ mixture is amorphous after film formation, but in the recording process, the light absorption layer generates heat by irradiation with laser light. When the light absorption layer generates heat, the ZnS—SiO ₂ mixture is densified or crystallized from an amorphous state having a low density. Here, the densification or crystallization temperature has a threshold value. Due to the threshold value, a portion within the beam diameter can be densified or crystallized. As a result, a fine shape change portion corresponding to the laser pulse can be formed. By increasing the density or crystallizing from a low-density amorphous state, the etching selectivity in the etching process can be increased, so that a fine convex structure can be formed over a large area.

  Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to the examples.

Example 1
An optical recording medium having the configuration shown in FIG.
Polycarbonate was used as the material of the support substrate 101, and its thickness was 0.6 mm.
ZnS—SiO ₂ (ZnS: SiO ₂ = 8: 2) was used as the material of the buffer layer 102, and the film thickness was 50 nm. Film formation was performed by sputtering. The composition of the sputtering target is ZnS 80 mol% and SiO ₂ 20 mol%.
AgInSbTe was used for the material of the light absorption layer 103, and the film thickness was 20 nm.
The convex structure 104 contains ZnS and SiO ₂ , the height of the convex structure from the upper surface of the light absorption layer is 50 nm, and the track direction period 105 is 200 nm.

The convex structure of the optical recording medium was reproduced by the method shown in FIG.
An objective lens with a numerical aperture of 0.85 and laser light with a wavelength of 405 nm were used, and the reproduction power was 1.5 mW.
As a result, a single period signal having a period of 200 nm corresponding to the convex structure was observed. The diffraction limit period of the laser beam used for reproduction is 238 nm (λ / (2 · NA)).
A period below the diffraction limit could be reproduced by irradiating the optical recording medium having the structure shown in FIG. 1A with light from the convex structure side and detecting a change in the amount of reflected light.

Example 2
An optical recording medium having the configuration shown in FIG.
Polycarbonate was used as the material of the support substrate 301, and its thickness was 0.6 mm.
ZnS—SiO ₂ (ZnS: SiO ₂ = 8: 2) was used as the material of the buffer layer 302, and the film thickness was 50 nm. Film formation was performed by sputtering. The composition of the sputtering target is ZnS 80 mol% and SiO ₂ 20 mol%.
SbTe was used as the material of the light absorption layer 303, and the film thickness was 20 nm.
The convex structure 304 contains ZnS and SiO ₂ , the height of the convex structure from the upper surface of the light absorption layer is 70 nm, and the track direction period 306 is 200 nm.
SiON was used as the material of the light transmission layer 305, and the film thickness was 150 nm.

The convex structure of the optical recording medium was reproduced by the method shown in FIG.
An objective lens with a numerical aperture of 0.85 and laser light with a wavelength of 405 nm were used, and the reproduction power was 1.0 mW.
As a result, a single period signal having a period of 200 nm corresponding to the convex structure was observed. The diffraction limit period of the laser beam used for reproduction is 238 nm (λ / (2 · NA)).
The period below the diffraction limit could be reproduced by irradiating the optical recording medium having the configuration shown in FIG. 2A with light from the light transmitting layer side and detecting the change in the amount of reflected light.

Example 3
Cylindrical convex structures were arranged as shown in FIG. 3 to produce an optical recording medium having a layer structure made of the same material as in Example 1.
The track direction recording period 503 was 250 nm, the track pitch 506 was 320 nm, and the diameter of the convex structure was changed according to the recording information. The maximum diameter 505 of the convex structure was 250 nm, and the diameter was changed in eight steps including the case where there was no convex structure.

The convex structure of the optical recording medium was reproduced by the method shown in FIG.
An objective lens with a numerical aperture of 0.85 and laser light with a wavelength of 405 nm were used, and the reproduction power was 1.5 mW.
FIG. 4A shows the mark arrangement. Reference numeral 502 denotes a convex structure, 503 denotes a recording period, and 504 denotes a beam moving direction. FIG. 4B shows changes in the reproduction signal level. Reference numeral 611 denotes a signal level sampled at the timing A in FIG. Reference numeral 612 denotes a signal level sampled at the timing H in FIG.
By sampling the signal at the timing of the period 503 of the convex structure, a reproduction signal whose signal level changes in eight steps according to the diameter was obtained.
Multi-level information at an 8-level level could be reproduced by the above-described optical recording medium configuration and reproduction method.

Example 4
An optical recording medium having a layer structure made of the same material as in Example 2 and having cylindrical convex structures arranged as shown in FIG. 5 was produced. The track direction period 703 was 137 nm, and the track pitch 706 was 119 nm. The diameter 705 of the convex structure was fixed at 60 nm. FIG. 6 shows the relationship between the arrangement of the convex structures and the reproduction signal level. FIG. 7 shows the cross-sectional shape of the medium. FIG. 8 is a top view of the medium showing the relationship between the convex structure row and the laser beam.

As shown in FIG. 7, a track (a, e) having no convex structure is provided every four tracks. By stacking the light transmission layer 905, a step for every three tracks was formed. As shown in FIG. 8, three tracks b, c, and d were reproduced simultaneously. As shown in FIG. 6A, the signal was sampled at the timing of the period 703 of the convex structure. In this case, the signal level changed depending on the number of convex structures included in the beam diameter 801. FIG. 6B shows changes in signal level. The signal level 811 indicates the signal level sampled at the timing A in FIG. The signal level 812 indicates the signal level sampled at the D timing in FIG. There exists a state from a state A in which seven convex structures are included in the beam diameter to a state in which there are no convex structures (not shown). As a result, a reproduction signal whose signal level changed in 14 steps was obtained.
In this way, by increasing the arrangement of the convex structures in the medium plane into a closely packed arrangement (three-fold symmetric arrangement) and simultaneously reproducing a plurality of structures, a high density can be achieved by narrowing the track pitch. .

Example 5
An optical recording medium was produced by the method shown in FIG.
First, each layer was formed in the lamination process shown in FIG.
A support substrate 1101 was formed of polycarbonate. Using ZnS-SiO ₂ is the buffer layer 1102, the film thickness was 50nm. Film formation was performed by sputtering. The composition of the sputtering target is ZnS 80 mol% and SiO ₂ 20 mol%.
The light absorption layer 1103 was formed of AgInSbTe so that the film thickness was 20 nm. The thin film 1104 to be a convex structure is ZnS—SiO ₂ , formed to have a film thickness of 100 nm, and set to λ / 4 (405 nm / 4≈100 nm). Film formation was performed by sputtering. The composition of the sputtering target is ZnS 80 mol% and SiO ₂ 20 mol%.
The sputtering method conditions for each layer were a film formation temperature of room temperature and a film formation atmosphere of Ar.

Next, in the recording step shown in FIG. 9B, information was recorded by irradiating laser light from the thin film side forming the convex structure. The wavelength of the laser beam used for recording is 405 nm, and the numerical aperture of the objective lens is 0.85. Reference numeral 1112 denotes a recording portion of ZnS—SiO ₂ . The recorded portion is crystallized or densified, and the unrecorded portion is amorphous and in a low density state.

Recording was performed by a laser light power level modulation method as shown in FIG.
The power level was modulated at two levels of P1 = 5 mW and P2 = 0.7 mW. T1 is a period during which the P1 level is maintained, that is, a pulse width. S indicates the pulse irradiation timing (recording cycle). T1 = 15 nsec and S = 57 nsec. Under these conditions, a single period signal having a period of 200 nm was recorded.

Next, in the etching step shown in FIG. 9D, the unrecorded portion of the thin film ZnS—SiO ₂ forming the convex structure after information recording was removed and processed into a convex shape. Reference numeral 1121 denotes a convex structure. The unrecorded portion was removed by solution etching. As the etching solution, a mixed solution of hydrofluoric acid (HF) and water (H ₂ O) was used. A 50% diluted solution was used for hydrofluoric acid. The solution ratio was HF: H ₂ O = 1: 2. The recording medium was immersed in the solution for 10 seconds. Immediately after the etching, the substrate was washed with water and dried with dry nitrogen or the like.
A recording medium having a convex structure was produced by the above method. By this method, it was possible to form a fine convex structure over a large area without a mask.

(A) It is explanatory drawing which shows an example of the 1st optical recording medium of this invention. (B) It is explanatory drawing which shows an example of the 1st reproducing | regenerating method of this invention. (C) It is explanatory drawing which shows the relationship between the laser intensity distribution of the incident laser beam, and the temperature distribution of the optical recording medium surface. (A) It is explanatory drawing which shows an example of the 2nd optical recording medium of this invention. (B) It is explanatory drawing which shows an example of the 2nd reproducing | regenerating method of this invention. (A) It is explanatory drawing (upward view) which shows an example of the 3rd optical recording medium of this invention. (A) It is explanatory drawing (upward view) which shows an example of the 3rd reproducing | regenerating method of this invention. (B) It is explanatory drawing which shows an example of the relationship between time and a signal level in the 3rd reproducing | regenerating method of this invention. It is explanatory drawing (upward view) which shows an example of the 4th optical recording medium of this invention. (A) It is explanatory drawing (upward view) which shows an example of the 4th reproduction | regeneration method of this invention. (B) It is explanatory drawing which shows an example of the relationship between time and a signal level in the 4th reproduction | regeneration method of this invention. It is explanatory drawing which shows an example of the 5th optical recording medium of this invention. (A) It is explanatory drawing (upward view) which shows an example of the 5th reproduction | regeneration method of this invention. (B) It is sectional drawing corresponding to (a) explanatory drawing (upward view) in the 5th reproduction | regeneration method of this invention. (A) It is explanatory drawing which shows an example of the lamination process of this invention. (B) It is explanatory drawing which shows an example of the recording process of this invention. (C) It is explanatory drawing which shows an example of the power level modulation method of a laser beam. (D) It is explanatory drawing which shows an example of an etching process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Support substrate 102 Buffer layer 103 Light absorption layer 104 Convex structure body 105 Period of convex structure body 201 Incident direction of laser light 202 Optical characteristic change region of light absorption layer 203 Convex structure body located at the center of beam 301 Support substrate 302 Buffer layer 303 Light absorption layer 304 Convex structure 305 Light transmission layer 306 Period of convex structure 401 Incident direction of laser light 402 Optical property change region of light absorption layer 403 Convex structure 501 located at the center of beam 501 Light Absorption layer 502 Convex structure 503 Track direction period of convex structure 504 Track center 505 Diameter of convex structure 506 Track pitch 60 Top view of recording medium 601 Laser beam 61 Change in signal level 611 A signal level 612 H Signal level at 701 Light absorption layer 702 Convex shape Structure 703 Period of convex structure in the track direction 704 Virtual lattice points of densely packed array 705 Diameter of convex structure 706 Track pitch 80 Top view of recording medium 801 Laser beam 802 Track center 81 Change in signal level 811 A Signal level at signal level 812 D 901 Support substrate 902 Buffer layer 903 Light absorption layer 904 Convex structure 905 Light transmission layer 906 Track pitch 100 Top view of recording medium 1001 Laser beam 101 Cross section of recording medium 110 Layer stacking process 1101 Support Substrate 1102 Buffer layer 1103 Light absorption layer 1104 Thin film forming convex structure 111 Information recording step 1111 Laser light incident direction 1112 Modified portion 1113 Laser light irradiation method 112 Unrecorded portion removal step 1121 Convex shape Structure

Claims (13)

  In an optical recording medium for recording and reproducing information by light, at least a thin-film light absorbing layer that absorbs reproducing light and generates heat, and a convex structure made of a material different from the light absorbing layer in contact with the light absorbing layer Are laminated on a support.   Using the optical recording medium according to claim 1, light is irradiated from the convex structure side to a laminate composed of a thin-film light absorption layer and a convex structure, and the amount of reflected light is changed. A method of reproducing an optical recording medium, comprising: detecting the optical recording medium.   In an optical recording medium that records and reproduces information by light, at least a thin-film light absorbing layer that absorbs reproducing light and generates heat, a convex structure that is in contact with the light absorbing layer, and transparency to the reproducing light. And an optical recording medium, wherein the optical transmission medium has a hemispherical shape following the convex structure.   Using the optical recording medium according to claim 3, light is irradiated from the light-transmitting layer side to a laminate composed of a thin-film light-absorbing layer, a convex structure, and a light-transmitting layer. A method for reproducing an optical recording medium, characterized in that a change in the optical recording medium is detected.   4. The optical recording medium according to claim 1, wherein the convex structure has a cylindrical shape, and the diameter of the convex structure changes according to recording information.   Using the optical recording medium according to claim 5, light is irradiated to a convex structure whose diameter changes according to recording information, and the amount of reflected light changes according to the period of the convex structure. A method of reproducing an optical recording medium, comprising: detecting the optical recording medium.   4. The convex structure according to claim 1, wherein the convex structure has a cylindrical shape, and the array of the convex structures in the optical recording medium plane is a finely packed array (three-fold symmetric array). Optical recording medium.   Using the optical recording medium according to claim 7, the convex structure is irradiated with light to simultaneously reproduce a plurality of track rows, and a change in the amount of reflected light is detected corresponding to the period of the convex structure. A method for reproducing an optical recording medium.   8. The optical recording medium according to claim 7, wherein the optical recording medium is a convex structure provided with a row in which no convex structure exists every n rows in the radial direction of the optical recording medium.   A method for reproducing an optical recording medium, wherein the optical recording medium according to claim 9 is used to simultaneously reproduce n-1 columns and detect the amount of reflected light.   10. The light according to claim 1, wherein the light absorption layer contains at least one element selected from Sb, Te, In, Bi, and Ga. recoding media. The optical recording medium according to any one of claims 1, 3, 5, 7, 9, and 11, wherein the convex structure contains ZnS and SiO ₂ .   Laminating step of forming a laminated body by laminating at least a thin film-shaped light absorption layer and a thin film material forming a convex structure on a supporting substrate, and irradiating light from the convex structure side to the laminated body And at least a recording step for recording information and a removing step for removing a non-recorded portion to form a convex structure body, according to any one of claims 1, 3, 5, 7, 9, 11, and 12. A manufacturing method of the optical recording medium described.

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