JP2002304772A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which is capable of exactly reading address information without impairing recording and reproducing characteristics, such as jitters, can be easily manufactured and can be provided with land prepits with high positional accuracy. SOLUTION: The surface continued with the opening of an LPP 38B is formed of an enveloping surface in contact with the flanks of n-pieces of column groups 40B1 to 40Bn by assuming n-pieces of the column groups 40B1 to 40Bn of which the centers at the base surfaces move to a land 34B side by as much as an increment Δr of the radii of the base surfaces and move to a groove 32B side by as much as a decrement Δr of the radii as the radii increase gradually along the groove 32B, then decrease gradually. The LPP having the enveloping surface described above can be formed by properly increasing and decreasing the beam diameter of the laser beam for scanning exposure of a photoresist in a mastering process step for manufacturing the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly, to an optical recording medium having a land / groove structure in which pits in which groove address information is recorded are formed in advance on lands.

[0002]

2. Description of the Related Art With the recent development of short wavelength lasers, digital versatile disks (DVs) capable of recording and reproducing data at a higher density than compact disks (CDs) have been developed.
D) has been put to practical use, and at present, DVD-R, which is a writable write-once optical recording medium, has also been put to practical use.

A guide groove for performing tracking at the time of recording is provided in advance on a substrate of a write-once optical recording medium.
A land / groove structure is formed. In the DVD-R, pits called prepits are formed in advance on the land, and the address information of the groove on the inner peripheral side of the land is recorded.

When a signal recorded on a DVD-R is reproduced by performing a tracking servo by a push-pull method, return light from a beam spot condensed on a groove is applied to the DVD-R.
The divided diodes A, B, C, and D are photoelectrically converted as detectors, and signals A,
B, C and D are obtained. The signal (A + B + C + D) obtained by adding the signals A, B, C, and D is a reproduced signal of the recorded signal. The signals A and B corresponding to the return light on the outer peripheral side and the signal C corresponding to the return light on the inner peripheral side. , D (A + BC)
-D) is a tracking error signal. Therefore, as shown in FIG. 6, the tracking error signal includes a negative pulse corresponding to the pre-pit of the land on the outer periphery of the groove and a positive pulse corresponding to the pre-pit of the land on the inner periphery of the groove. appear. Usually, the land records the address information of the groove on the inner circumference side,
By detecting the pre-pit signal that appears as a negative pulse, the recorded address information can be read.

In order to accurately read address information,
It is necessary to increase the pre-pit signal strength, and it is necessary to form a pre-pit of a certain size. For this reason, for example, as shown in FIG.
Usually, prepits opened on both sides of an adjacent groove are formed, such as forming prepits 4b opened on both sides of the grooves 3a and 3b for recording address information of the groove 3b. In this way, the overlap between the pre-pit and the recording beam spot 5 is increased, and the pre-pit signal intensity is increased.

[0006]

However, when viewed from the groove, the prepit formed on the land is like a groove branched from the groove, and the material of the recording layer expands when the pit is formed on the recording layer. Therefore, there is a problem that a desired pit length cannot be obtained and recording cannot be performed accurately (jitter increases). Also,
If the pre-pit signal is too strong, it causes noise to the RF signal. Further, in an optical disc having a higher recording density by narrowing a track pitch, there is a problem that a prepit signal leaks into an adjacent track.

Japanese Patent Application Laid-Open No. 2000-11460 discloses an optical recording medium in which prepits are formed at positions that do not overlap on adjacent tracks and are shifted to the groove side that forms a pair with the center position of the land. Has been described. In this optical recording medium, as shown in FIG. 8, for example, the pre-pits 4b are formed on the lands 2b of the substrate 1 at positions deviated toward the grooves 3b which are pairs with the lands 2b. In this case, it is not affected by the prepits 4a adjacent on the inner peripheral side.

Japanese Patent Laid-Open Publication No. 2000-187887 describes an optical recording medium capable of obtaining a stable preformat signal by forming a prepit while leaving a part on the inner circumference or the outer circumference of a land. Have been.
Also in this optical recording medium, for example, as shown in FIG.
Of the land 3b, which is a pair with the land 2b,
Since the pre-pits 4b are formed while notching the side and leaving a part on the groove 3c side, the recording beam spot 5 is formed.
Are not affected by the prepits 4a adjacent on the inner peripheral side when scanning. Further, in this optical recording medium, by setting the groove width Wp and length Lp of the pre-pits within a predetermined range, leakage of the pre-pit signal to an adjacent track is prevented.

A substrate having a land / groove structure and formed with prepits is manufactured using a mold called a stamper having fine irregularities formed on the surface. This stamper is a duplicate of a metal master. The metal master is a mastering process of writing and developing predetermined data for forming grooves and pre-pits with a laser beam on a photoresist formed on a glass substrate or the like. Has been produced.

However, in order to provide pre-pits in which the lands of the substrate are cut out in a rectangular or semi-circular shape as in the above-described optical recording medium, photo-forming is divided into two steps, one for forming grooves and the other for forming pre-pits. It is necessary to expose the resist, but there is a problem that the pre-pit position accuracy cannot be improved because the exposure is performed twice.

Accordingly, it is an object of the present invention to be able to accurately read address information without impairing recording / reproducing characteristics such as jitter, to facilitate manufacture, and to provide land prepits with high positional accuracy. An optical recording medium is provided.

[0012]

In order to achieve the above object, an optical recording medium according to the present invention is formed such that grooves are formed in a spiral or concentric manner and adjacent to lands existing between adjacent grooves. An optical recording medium in which pits are formed only in one groove side of a groove and in which pits in which information of the one groove is recorded are formed in advance, and a surface continuous with the opening is gradually reduced in radius of a bottom surface along the groove. As the diameter gradually increases and then gradually decreases, the center of the bottom surface moves toward the land more than the increase in the radius and moves toward the groove less than the decrease in the radius, and contacts the side surface of the cylinder group. It is characterized by being formed by an envelope surface.

According to the optical recording medium of the present invention, the surface continuous to the opening of the pit (land pre-pit) formed in advance on the land is formed by gradually increasing and decreasing the radius of the bottom surface along the groove. Assuming a group of cylinders in which the center of the bottom surface moves to the land more than the increase in radius and moves to the groove less than the decrease in radius, a major feature is that it is formed by an envelope surface in contact with the side surface of the cylinder group. is there. The land prepit having such a shape can be formed by appropriately increasing or decreasing the beam diameter of a laser beam for scanning and exposing a photoresist in a mastering step for manufacturing a substrate. Therefore, with one exposure, the photoresist can be exposed corresponding to both the groove formation and the pre-pit formation, so that the manufacturing process can be simplified and the positional accuracy of the land pre-pit can be improved.

Further, since the land prepits are opened only on one groove side of the adjacent groove and not opened on the other groove side, when a pit is formed on the recording layer of the other groove. The land serves as a wall to prevent the recording layer material from expanding and extending to the land prepit. Therefore, a desired pit length can be obtained, and accurate recording can be performed. Further, since the land prepit is formed from one of the adjacent grooves, a pulse necessary for reading the address information out of the land prepit signal becomes large, and a pulse unnecessary for reading the address information disappears. (Or smaller). For this reason, the address information can be read accurately, and noise to the RF signal can be reduced.

In the above-mentioned optical recording medium, the center of the bottom surface moves to the land side more than the radius increase and the groove side to the groove side less than the radius decrease when forming the surface continuous with the opening of the land prepit. Assume a group of moving cylinders,
It is preferable to move the center of the bottom surface of the column group to the land side by 10 nm or more in addition to the increase in radius, and more preferable to move the center to the land side by 20 nm or more in addition to the increase in radius.
When the center of the bottom surface moves to the land side more than the radius increase, the land facing the opening of the land prepit protrudes toward the opening side, and the pulse necessary for reading address information in the land prepit signal is As a result, the address information can be read more accurately.

When the width of the land where no pits are formed in advance is the normal land width a and the land width of the narrowest portion where the pits are formed in advance is the narrowest land width b, (ab) Is multiplied by the pit length Lp represented by the distance between two points at which the tangent of the envelope surface and the inner circumference of the land intersect at the largest angle, is 0.12 μm.
It is preferably not less than m ^{2 and not} more than 0.27 μm ² . The lower limit is more preferably 0.13 [mu] m ^2, 0.14 .mu.m ² is more preferable. The upper limit is more preferably 0.25 [mu] m ^2, 0.23 .mu.m ² is more preferable.

The product of the pit width Wp and the pit length Lp of the land pre-pit corresponds to the cross-sectional area of the land pre-pit on the substrate surface. Is preferably equal to the spot area of the recording beam. If the cross-sectional area of the land pre-pit is too large, the land pre-pit signal becomes too large, causing noise to the RF signal. On the other hand, if the cross-sectional area of the land pre-pit is too small, the land pre-pit signal cannot be detected accurately.

In this case, if the pit length Lp is too long even with the same area, the overlap with the spot of the recording beam becomes small, so that the pit length Lp is 0.3 μm or more and 3.0 or more.
μm or less is preferred. The lower limit is more preferably 0.5 μm, and even more preferably 0.7 μm. Further, the upper limit is more preferably 2.2 μm, and still more preferably 1.7 μm.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a DVD-R type optical recording medium having a recording layer only on one side will be specifically described with reference to the drawings.

As shown in FIG. 1, a DVD-R type optical recording medium 10 is provided with a transparent disk-shaped substrate 12 formed with a groove having a track pitch of 0.6 to 0.9 μm. A laminate 20 in which a dye-containing recording layer 14, a reflective layer 16, and a protective layer 18 are formed in this order on the side surface
A disk-shaped protective substrate 22 having substantially the same dimensions as the substrate 12 of the laminate 20 is bonded with an adhesive 24. Hereinafter, the configuration of the optical recording medium 10 will be described according to the manufacturing process.

A tracking groove is formed on the substrate 12 to form a land / groove structure. This groove is preferably formed directly on the substrate at a predetermined track pitch when a resin material such as polycarbonate is injection-molded or extruded. The depth of the groove is preferably in the range of 80 to 300 nm, and 100 to 250 n.
The range of m is more preferred. Also, the half width is 0.2 to
It is preferably in the range of 0.9 μm.

FIG. 2 is a view of the substrate 12 as viewed from above.
As shown in FIG. 2, a land 34A is provided on the outer peripheral side of the groove 32A, and a land 34B is provided on the outer peripheral side of the groove 32B.
However, lands and grooves are alternately arranged such that lands 34C are arranged on the outer peripheral side of the groove 32C. A land pre-pit (LPP) 38B in which address information of the groove 32B is recorded is formed on a land 34B between the adjacent grooves 32A and 32B. Similarly, an LPP 38A recording address information of the groove 32A is formed on the land 34A, and an LPP 38C recording address information of the groove 32C is formed on the land 34C. As described above, the address information of each groove is recorded by forming the LPP on the land on the outer peripheral side. In the present invention, the shape and position of the LPP are important.

LPP 38B provided on land 34B
Has an opening 36B only on the side wall on the groove side (groove 32B side on the inner peripheral side) for recording address information, and has an opening on the other side wall on the groove side (groove 32C side on the outer peripheral side). Not. By providing an opening only on the side wall on the groove side for recording the address information, when a pit is formed in the recording layer, the land on the non-opening side expands the recording layer material due to expansion of the LPP. The pit length can be prevented, and a desired pit length can be obtained.

The LPP38B has been described as an example.
The same applies to PP38A and LPP38C (the same applies hereinafter).

Here, the shape of each LPP will be described. As shown in FIGS. 3A and 3B, the LPP38B
The center of the bottom surface moves toward the land 34B by the radius increment Δr as the radius of the bottom gradually increases and then gradually decreases along the groove 32B, and the radius decreases Δr along the groove 32B. only assuming n number of cylinder group 40B ₁ ~40B _n to move to the groove 32B side, it is formed in the envelope surface in contact with the side surfaces of the n cylinder group 40B ₁ ~40B _n.

In the mastering process for manufacturing a substrate, the LPP having the above-mentioned envelope surface is formed by observing a laser beam for scanning and exposing a photoresist to a group of cylinders and scanning and exposing a groove portion. As the beam radius of the laser beam gradually increases and then gradually decreases, the photoresist is moved so that the center of the beam spot moves to the land side by the increased radius and moves to the groove side by the decreased radius. It can be formed by scanning exposure, and the positional accuracy of the LPP can be improved.

As shown in FIG. 2, LPP38B
Is adjacent to the grooves 32A and 32B, but is closer to the groove 32B than the center line of the land 34B indicated by a dashed line.
It is formed from the side. Recording beam spot 42
Moves along the center line of the groove 32B indicated by the broken line, the spot 42 of the recording beam and the groove 32B move.
The overlap between the spot 42 and the LPP 38C formed on the inner land 34C is minimized so that the overlap with the LPP 38B formed on the outer land 34B for recording the address information of B is as small as possible.
It is preferable to dispose the LPP 38B on the land 34B and dispose the LPP 38C on the land 34C. By forming the LPP so as to be closer to the groove on which the address information is recorded, the pulse required for reading the address information in the LPP signal increases, and the pulse unnecessary for reading the address information decreases. In particular, by forming the LPP on the groove side relative to the center line of the land, it is possible to increase or decrease the beam diameter of the laser beam for scanning and exposing the photoresist without lowering the scanning speed in the mastering process for manufacturing the substrate. it can.

As shown in FIG. 4, the width of the land where no LPP is formed (normal land width) is a, and the land width of the narrowest part where the LPP is formed (narrowest land width) is b. At this time, the ratio (b / a) of the narrowest land width b to the normal land width a is preferably 0.4 or more.
5 or more is more preferable. For example, if the normal land width is 0.
For a land of 4 μm, the narrowest land width is preferably at least 0.16 μm, more preferably at least 0.20 μm.

The distance represented by (ab) is represented by LPP
And the distance between the points c and d when the point where the tangent of the envelope and the inner circumference of the land intersect at the largest angle is the length Lp of the LPP. The approximate cross-sectional area of the LPP on the surface can be represented by the product Sp of the width Wp of the LPP and the length Lp of the LPP.

The product Sp of the width Wp of the LPP and the length Lp of the LPP is preferably not less than 19% and not more than 44% of the area of the beam spot having a diameter at which the recording energy becomes 1 / e ² . Below 19%, the strength of the LPP signal is reduced,
The LPP signal cannot be detected accurately. Meanwhile, 4
If it exceeds 4%, the LPP signal becomes too large, causing noise to the RF signal. For example, if the area of the recording beam spot is 0.62 μm ² , the product Sp is 0.1
The thickness is preferably ² μm ² or more and 0.27 μm ² or less. The lower limit is more preferably 0.13 [mu] m ^2, 0.14 .mu.m ² is more preferable. The upper limit is more preferably 0.25 [mu] m ^2, 0.23 .mu.m ² is more preferable. The diameter at which the recording energy becomes 1 / e ² is 0.82 × wavelength / N.
A, for example, wavelength 650 nm, NA (numerical aperture)
At 0.6, the diameter is 0.888 μm.

In this case, if the pit length Lp is too long even with the same area, the overlap with the recording beam spot becomes small. Therefore, the upper limit of the pit length Lp is 3.0 times the longitudinal length of the recording beam spot. Or less, more preferably 2.0 times or less. Further, the lower limit of the pit length Lp is preferably at least 0.5 times, more preferably at least 1.0 times the length of the recording beam spot in the longitudinal direction. For example, when the longitudinal diameter of the recording beam spot is 0.4 to 0.9 μm, the pit length Lp of the LPP is preferably 0.3 μm or more and 3.0 μm or less. The lower limit is more preferably 0.5 μm, and even more preferably 0.7 μm. Further, the upper limit is more preferably 2.2 μm, and still more preferably 1.7 μm.

Examples of the material used for the substrate 12 (including the protective substrate 22) include glass; polycarbonate; acrylic resins such as polymethyl methacrylate; polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymer; An amorphous polyolefin and a polyester, which may be used in combination if desired. Note that these materials can be used in the form of a film or a rigid substrate. Among the above materials, polycarbonate is preferred from the viewpoints of moisture resistance, dimensional stability, cost, and the like. The substrate has a diameter of 120
Those having a thickness of ± 3 mm and a thickness of 0.6 ± 0.1 mm, or a diameter of 80 ± 3 mm and a thickness of 0.6 ± 0.1 mm are generally used.

On the surface of the substrate 12 on the side where the recording layer 14 is provided, the flatness is improved, the adhesive strength is improved, and the recording layer 1 is formed.
For the purpose of preventing the deterioration of No. 4, an undercoat layer may be provided. Examples of the material of the undercoat layer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer, polyvinyl alcohol, N
-Methylol acrylamide, styrene / vinyl toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, polyethylene ,
Examples include polymer substances such as polypropylene and polycarbonate; and surface modifiers such as silane coupling agents.

The undercoat layer is prepared by dissolving or dispersing the above substances in an appropriate solvent to prepare a coating solution, and then applying the coating solution to the surface of the substrate by using a coating method such as spin coating, dip coating, or extrusion coating. Can be formed. The thickness of the undercoat layer is generally 0.00
In the range of 5 to 20 μm, preferably 0.01 to 10
It is in the range of μm.

A dye-containing recording layer 14 is provided on the surface of the substrate 12 (or undercoat layer) on which the groove is formed. Examples of the dye include a cyanine dye, an azo dye, a phthalocyanine dye, an oxonol dye, and a pyrromethene dye.A cyanine dye, an azo dye, and an oxonol dye are preferable.
Oxonol dyes are particularly preferred.

The dye-containing recording layer 14 is formed by, for example, dissolving a cyanine dye and, if desired, an anti-fading agent and a binder in a solvent to prepare a coating solution, and then applying the coating solution to a groove of a substrate. It can be carried out by applying it to the surface to form a coating film and then drying.

Solvents for the coating solution for forming the dye-containing recording layer include esters such as butyl acetate and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone;
Chlorinated hydrocarbons such as dichloroethane and chloroform; amides such as dimethylformamide; hydrocarbons such as cyclohexane; ethers such as tetrahydrofuran, ethyl ether and dioxane; ethanol, n-propanol, isopropanol, n-butanol and diacetone alcohol. Alcohols such as 2,2,3,3-tetrafluoropropanol; and glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether. The above solvents can be used alone or in combination of two or more in consideration of the solubility of the compound to be used. Various additives such as an antioxidant, a UV absorber, a plasticizer, and a lubricant may be further added to the coating solution according to the purpose.

Representative examples of the anti-fading agent include nitroso compounds, metal complexes, diommonium salts, and aminium salts. These examples are described, for example, in JP-A-2-300288 and JP-A-3-224793.
Or each of the publications such as JP-A No. 4-146189. When an anti-fading agent is used, its amount is usually in the range of 0.1 to 50% by weight, preferably in the range of 0.5 to 45% by weight, more preferably in the amount of the dye. Ranges from 3 to 40% by weight, in particular from 5 to 25% by weight.

Examples of the binder include natural organic high-molecular substances such as gelatin, cellulose derivatives, dextran, rosin and rubber; and hydrocarbon resins such as polyurethane, polyethylene, polypropylene, polystyrene and polyisobutylene; polyvinyl chloride Vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride / polyvinyl acetate copolymer; acrylic resins such as polymethyl acrylate and polymethyl methacrylate; polyvinyl alcohol, chlorinated polyethylene, epoxy resin, butyral resin, rubber derivatives And synthetic organic polymers such as precondensates of thermosetting resins such as phenol-formaldehyde resins. When a binder is used in combination as the material of the recording layer 14, the binder is used in an amount of 0.2 to 20 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the dye.
More preferably, it is 1 to 5 parts by weight. The concentration of the dye in the coating solution thus prepared is generally 0.01 to 10
% By weight, preferably in the range of 0.1 to 5% by weight.

Examples of the coating method include a spray method, a spin coating method, a dipping method, a roll coating method, a blade coating method, a doctor roll method, and a screen printing method. The dye-containing recording layer 14 may be a single layer or a multilayer. The layer thickness of the dye-containing recording layer 14 is generally 20 to 500.
nm, preferably in the range of 50-300 nm. In the optical disc of the present invention, the dye-containing recording layer 14
Has a thickness of 130 to 200 nm (more preferably 140 to 190 nm, particularly preferably 145 nm) in the groove.
To 185 nm). The thickness of the dye-containing recording layer 14 at the land is 50 to 15
It is preferably in the range of 0 nm (more preferably, 60 to 120 nm).

On the recording layer 14, a reflective layer 16 is provided for the purpose of improving the reflectivity particularly when information is reproduced. The light-reflective substance that is the material of the reflective layer 16 is a substance having a high reflectivity to laser light.
g, Se, Y, Ti, Zr, Hf, V, Nb, Ta, C
r, Mo, W, Mn, Re, Fe, Co, Ni, Ru,
Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, C
d, Al, Ga, In, Si, Ge, Te, Pb, P
Metals and semimetals such as o, Sn, Bi, and stainless steel can be mentioned. Preferred among these are Cr, Ni, Pt, Cu, Ag, Au, Al and stainless steel. These substances may be used alone, or in combination of two or more kinds, or as an alloy. The reflection layer 16 can be formed on the recording layer 14 by, for example, vapor deposition, sputtering, or ion plating of the above-mentioned reflective substance. The thickness of the reflective layer 16 is generally in the range of 10 to 800 nm, preferably in the range of 20 to 500 nm, and more preferably in the range of 50 to 300 nm.

On the reflective layer 16, a protective layer 18 is provided for the purpose of physically and chemically protecting the recording layer 14 and the like. The protective layer 18 may be provided on the side of the substrate 12 where the recording layer 14 is not provided, for the purpose of improving scratch resistance and moisture resistance. As a material used for the protective layer 18,
For example, SiO, SiO ₂ , MgF ₂ , SnO ₂ , Si ₃ N
Inorganic substances such as ₄ , thermoplastic resin, thermosetting resin, UV
An organic substance such as a curable resin can be used. In addition,
The protective layer 18 does not necessarily have to be provided.

The protective layer 18 can be formed, for example, by laminating an adhesive layer on the reflective layer 16 and / or the substrate 12 on a film obtained by extrusion of a plastic. Or vacuum deposition, sputtering,
It may be provided by a method such as coating. In the case of a thermoplastic resin or a thermosetting resin, these are dissolved in an appropriate solvent to prepare a coating solution, and then the coating solution is applied.
It can also be formed by drying. In the case of a UV curable resin, a coating solution is prepared as it is or dissolved in an appropriate solvent, and then the coating solution is applied,
It can also be formed by irradiating light and curing. Various additives such as an antistatic agent, an antioxidant, and a UV absorber may be added to these coating solutions according to the purpose. The thickness of the protective layer 18 is generally 0.1 to 10
It is in the range of 0 μm.

According to the above steps, the recording layer 1 is formed on the substrate 12.
4, a laminate 20 provided with the reflective layer 16 and the protective layer 18 can be manufactured. The obtained laminated body 20 and a disk-shaped protective substrate 22 having substantially the same dimensions as the substrate 12 of the laminated body 20 are bonded with an adhesive 24 so that the recording layer 14 is on the inside, so that recording is performed only on one side. DVD-R with layers
The optical recording medium 10 of the mold can be manufactured. As the adhesive, the UV curable resin used for forming the protective layer 18 may be used, or a synthetic adhesive may be used.
Further, a double-sided tape or the like may be used. It is preferable that the thickness of the optical recording medium after bonding is adjusted to be 1.2 ± 0.2 mm.

Recording and reproduction of the obtained DVD-R type optical recording medium are performed, for example, as follows. First, while rotating the optical recording medium at a predetermined constant linear velocity (3.84 m / sec) or a predetermined constant angular velocity, a recording laser light such as a semiconductor laser light is focused from the substrate side through an optical system,
Irradiate. Irradiation of the laser beam causes the irradiated portion of the recording layer to absorb the light and locally increase the temperature, thereby causing a physical or chemical change to change its optical characteristics, thereby recording information. The recording light is a laser light in the visible region, usually 600 nm to 700 nm (preferably 620 to 700 nm).
A semiconductor laser beam having an oscillation wavelength in the range of 680 nm (more preferably, 630 to 660 nm) is used. The recording light is preferably collected through an optical system having an NA of 0.55 to 0.7.

The information recorded as described above is reproduced by irradiating a semiconductor laser beam having the same wavelength as at the time of recording from the substrate side while rotating the optical recording medium at a predetermined constant linear speed, and reflecting the reflected light. It can be performed by detecting.

As described above, in the optical disk of this embodiment, the center of the bottom surface is gradually changed along the groove as the radius of the bottom surface gradually increases and then gradually decreases along the groove. Assuming a group of cylinders that move to the land side more than the increase in radius and move to the groove side below the decrease in radius, they are formed by an envelope surface in contact with the side surface of the group of cylinders. Land pre-pit
In a mastering step for manufacturing a substrate, the photoresist can be formed by appropriately increasing or decreasing the beam diameter of laser light for scanning and exposing a photoresist. Therefore, with one exposure, the photoresist can be exposed corresponding to both the groove formation and the pre-pit formation, so that the manufacturing process can be simplified and the positional accuracy of the land pre-pit can be improved.

The land prepit has an opening only on one groove side of an adjacent groove, and has no opening on the other groove side. Therefore, pits are formed on the recording layer of the other groove. In this case, the lands serve as walls to prevent the recording layer material from expanding and extending to the land prepits. Therefore, a desired pit length can be obtained, and accurate recording can be performed. Further, in the present invention, since the land pre-pit is formed from one of the adjacent grooves, the pulse required for reading the address information out of the land pre-pit signal is large, and is unnecessary for reading the address information. Such a pulse disappears (or becomes smaller). For this reason, the address information can be read accurately, and noise to the RF signal can be reduced.

In the above description, as the radius of the bottom surface gradually increases along the groove and then gradually decreases along the groove, the center of the bottom surface moves toward the land by the increased radius. In addition, assuming a group of cylinders that move toward the groove by an amount corresponding to the decrease in the radius, an example in which the cylinder is formed by an envelope surface that is in contact with the side surface of the group of cylinders has been described. In addition, assuming a group of cylinders that move to the groove side within the radius decrease or less, an envelope surface that is in contact with the side surface of the group of cylinders can be used.

For example, as shown in FIG.
The center of the bottom surface has a radius increase Δr + α (more than the increase) land 3 as the radius of the bottom surface gradually increases and then gradually decreases along the groove 32B along the groove 32B.
N column groups 40B ₁ that move to the 4B side and decrease in radius Δr + α (less than the decrease) to the groove 32B side
Assuming ～40B _n, formed in the envelope surface in contact with the side surfaces of the n cylinder group 40B ₁ ~40B _n.

As described above, when the center of the bottom surface moves to the land side by more than the increase of the radius, the land portion facing the opening of the land prepit protrudes toward the opening side, and the address information of the land prepit signal is The pulse required for reading the address becomes large, and the address information can be read more accurately. On the other hand, when the land portion facing the opening of the land prepit is recessed on the side opposite to the opening side, a pulse necessary for reading address information out of the land prepit signal becomes small.

When assuming a column group, the increase in radius is
In addition, it is preferable to move to the land side more than 10nm at the maximum.
In addition to the increase in radius, move to the land side by 20 nm or more.
It is more preferable to move. That is, the land
The maximum value α of α _MAXIs preferably 10 nm or more.
More preferably, the thickness is 20 nm or more. Conversely, the maximum value α
_{M AX}Is not preferred to be a negative value.

In the above description, a laminate having a dye-containing recording layer, a reflective layer, and a protective layer provided on the substrate surface,
An example of a DVD-R type optical recording medium having a recording layer on only one side and having a structure in which a disc-shaped protective substrate having substantially the same dimensions as a substrate and a recording layer on the inner side are joined is described. Is
Two laminates having a dye-containing recording layer, a reflective layer, and a protective layer provided on the substrate surface were prepared, and recording was performed on both sides of a structure in which the two laminates were joined such that each recording layer was on the inside. The present invention can also be applied to a DVD-R type optical recording medium having a layer.

In the above description, an example of a DVD-R type optical recording medium has been described. However, the present invention can be applied to an optical recording medium capable of recording address information by LPP. The present invention can also be applied to a rewritable digital video disk such as a DVD-RW, a CD-R, and an MO.

In the above description, an example has been described in which the address information of the groove on the inner peripheral side of the land is recorded as the LPP signal. However, the information recorded on the land is not limited to the address information as long as it corresponds to the groove. For example, synchronization information for position search may be used. Further, the land may record the information of the groove on the outer peripheral side as an LPP signal.

[0056]

[Example 1] A polycarbonate substrate having a spiral groove (land) and LPP formed on the surface thereof by injection molding (thickness: 0.6 mm, outer diameter: 120 m)
m, inner diameter: 15 mm, manufactured by Teijin Limited, trade name “Panlite AD5503”).

The groove depth, groove width, groove pitch, and width of the groove inclined portion of the groove are as follows. The groove depth D _{g of} the groove, the groove width W _g , and the width of the groove inclined portion (W _g1 −W _g2 ) / 2 are:
Each is defined as shown in FIG. The measurement of the groove depth, the groove width, the groove pitch, and the width of the groove inclined portion was performed by an atomic force microscope (AFM).

Groove depth Dg: 145 nm Groove width Wg: 300 nm Groove pitch: 740 nm Groove inclined portion width (W _g1 −W _g2 ) / 2: 50 nm (25 on one side)
nm) The average value of the land width (normal land width a) is 0.44 μm
In this land, an LPP having an opening only on the inner groove side is formed. The LPP has a predetermined envelope surface, and as shown in FIG.
29 μm, LPP length Lp is 1.1 μm, LPP width Wp
Is 0.15 μm, the protruding width α _MAX of the land portion facing the LPP is 0.07 μm, the LPP length Lp and the LPP width W
The product Sp with p was 0.165 μm ² .

1 g of a dye obtained by mixing the following oxonol dye (A) and oxonol dye (B) at a ratio of 4: 1,
2,2,3,3-tetrafluoro-1-propanol 1
The coating solution for forming a light absorbing layer was applied onto the groove surface of the obtained substrate at a rotation speed of 300 to 3000 r.
pm while applying by spin coating,
It dried and the light absorption layer was formed. The thickness of the light absorbing layer was 95 nm in the groove and 55 nm in the land as measured by observing the cross section of the light absorbing layer by SEM.

[0060]

Embedded image

Next, by DC sputtering in an argon atmosphere, A
g was formed. The pressure in the chamber was 0.5 Pa.

Further, a UV curable resin (trade name “SD-318”, manufactured by Dainippon Ink and Chemicals, Inc.) is provided on the reflective layer.
Is annularly dispensed, and a separately prepared polycarbonate disk-shaped protective substrate (diameter: 120 mm, thickness: 0.1 mm) is provided.
6mm) and centered on each other,
By rotating at 0 rpm for 3 seconds, the UV curable resin was spread over the entire surface and excess UV curable resin was shaken off. When the UV-curable resin was spread over the entire surface, the UV-curable resin was cured by irradiating ultraviolet rays with a high-pressure mercury lamp, and the substrate on which the light absorbing layer and the reflective layer were formed and the disc-shaped protective substrate were bonded. The thickness of the bonding layer was 25 μm, and the bonding could be performed without air bubbles.

By the above steps, the DVD-ROM according to the present invention
An R-type optical disk was manufactured. In the above-described mastering process for manufacturing a substrate, a single exposure can expose the photoresist to both the groove formation and the pre-pit formation, thereby simplifying the manufacturing process. Also,
The unrecorded LPP block error value was as low as 0.5%, and the LPP could be formed with extremely high positional accuracy.

Comparative Example 1 A DVD-R type optical disc for comparison was obtained in the same manner as in Example 1 except that an LPP formed at the center of the land portion of the substrate and having no opening was formed. The LPP length Lp and the LPP width Wp are both 0.
15 μm. In the mastering step for manufacturing the substrate, the photoresist was exposed to two beams for forming grooves and for forming prepits. In addition, unrecorded LPP
The block error value shows a large value of 3.5%, and LPP
Was not as high as in Example 1.

Comparative Example 2 A DVD-R type optical disc for comparison was obtained in the same manner as in Example 1 except that the LPP was formed so as to have openings on both groove sides adjacent to the land portion of the substrate. Was. The shape of the LPP is a notch with both sides chipped as shown in FIG. 7, and the LPP length Lp is 0.22.
μm. In the mastering process for substrate fabrication,
The photoresist was exposed with two beams for forming grooves and for forming prepits. Further, the LPP block error value before recording was as large as 4.0%, and the positional accuracy of LPP was not as high as that of the first embodiment.

[Examples 2 to 7] LPP length Lp, LPP
Product Sp of the width Wp, protruding width of the land portion facing the LPP alpha _{MA X,} and LPP length Lp and LPP width Wp
A DVD-R type optical disc according to the present invention was manufactured in the same manner as in Example 1 except that the following was changed.

[Measurement of LPP Signal Strength Before Recording] With respect to the DVD-R type optical discs of the above embodiment and comparative example,
From the amplitude of the convex signal to the push-pull signal, LP before recording
The P signal intensity (LPPb) was measured. LPPb is 0.1
8-0.26 is the standard range. Table 1 shows the obtained results.

[Evaluation as Optical Disk] The DVD-R type optical disks of the above embodiment and the comparative example were added to the DDU100.
Using a 0 (manufactured by Pulstec) evaluator, a DVD modulation signal was recorded at a recording power of 9 mW with a laser beam wavelength of 650 nm (pickup at NA 0.6), a constant linear velocity of 3.5 m / s. About the optical disc after recording,
Jitter was measured using a Packard modulation domain analyzer “53310A”. The smaller the jitter value is, the smaller the pit variation is, and the specification range is 8.0% or less. Table 1 shows the obtained results.

[Block Error Value of LPP Signal Before Recording] The block error value (LLP block error) of the land pre-pit signal was measured for the DVD-R type optical disks of the above embodiment and the comparative example before recording. The LPP and the wobble maintain a fixed phase relationship, and if the phase of the LPP and the wobble deviate, it becomes difficult to accurately detect the LPP, and an error in LPP decoding increases. That is, the block error value is a measure of the position accuracy of the LPP.

[Aperture Ratio of LPP Signal after Recording] The aperture ratio (AR) of the land pre-pit signal was measured for the DVD-R type optical disks of the above-described Example and Comparative Example after recording. The aperture ratio is the height when the signal becomes minimum. AR is within a standard range of 15% or more.

[0071]

[Table 1]

From the results in Table 1, it can be seen that the DVD-R according to the present invention
Type optical discs (Examples 1-4), LPPb
Is as large as 0.18 or more and AR is as high as 16% or more, which is sufficient for detecting address information. In addition, it can be seen that the jitter value is as small as about 7.5% and stable recording / reproducing characteristics can be obtained. Furthermore, the unrecorded LPP block error value shows a low value of 0.1% to 0.6%, indicating that the LPP is formed with extremely high positional accuracy.

Further, as in the fifth embodiment, the LPP length Lp
When the product Sp of the LPP width and the LPP width Wp is too small, the LPPb slightly decreases. As in the sixth embodiment, when the product Sp is too large, the jitter increases to 8.1%. Further, as in Example 7, the protruding width alpha _{MA X} of the land portion becomes negative,
The value of AR drops to 12%.

On the other hand, in the case of the DVD-R type optical disc for comparison of Comparative Example 1, the jitter value was as large as 8.3%, and satisfactory recording / reproducing characteristics such as easy reading error of the digital signal were likely to occur. It turns out that it cannot be obtained. Also, in the case of the optical disk of Comparative Example 2, the jitter value was 8.7%.
As in Comparative Example 1, it can be seen that satisfactory recording / reproducing characteristics cannot be obtained, for example, reading errors of digital signals are likely to occur. In addition, the LPP block error value before recording is as large as 3.5% in Comparative Example 1 and 4.0% in Comparative Example 2, indicating that the positional accuracy of LPP is not as high as that of the optical disk of Example. .

[0075]

According to the optical recording medium of the present invention, the address information can be read accurately without impairing the recording / reproducing characteristics such as jitter, the manufacturing process can be simplified, and the land pre-pits can be read. This has the effect of being able to be formed with high positional accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a laminated structure of an optical recording medium according to an embodiment.

FIG. 2 is a plan view of a part of the substrate of the optical recording medium according to the present embodiment as viewed from above.

FIG. 3A is a perspective view for explaining a shape of a surface continuous with an opening of a land prepit, and FIG. 3B is a plan view.

FIG. 4 is a plan view for defining a width and a length of a land prepit.

FIG. 5 shows the shape of a surface that is continuous with the opening of the land prepit.
FIG. 3 is a plan view for explaining a shape of a surface facing an opening.

FIG. 6 is a waveform diagram of a land pre-pit signal. FIG. 4 is a schematic diagram for defining a groove depth, a groove width, a groove pitch, and a width of a groove inclined portion of a groove.

FIG. 7 is a perspective view of a substrate portion of a conventional optical recording medium provided with land prepits.

FIG. 8 is a perspective view of a substrate portion of a conventional optical recording medium provided with land prepits.

FIG. 9 is a perspective view of a substrate portion of a conventional optical recording medium provided with land prepits.

FIG. 10 is a schematic diagram for defining a groove depth, a groove width, a groove pitch, and a width of a groove inclined portion of a groove.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical recording medium 12 Substrate 14 Recording layer 16 Reflective layer 18 Protective layer 20 Laminated body 22 Protective substrate 24 Adhesive 32A-C Groove 34A-C Land 36A-C Opening 38A-C LPP 42 Spot

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D029 WA02 WA36 5D090 AA01 BB03 BB05 CC14 EE02 GG03 GG09

Claims (4)

[Claims] A groove is formed spirally or concentrically, and an opening is formed in a land existing between adjacent grooves only on one side of the adjacent groove to record information of the one groove. An optical recording medium in which pits have been formed in advance, and the center of the bottom surface is more than the radius increase as the radius of the bottom surface gradually increases after the radius of the bottom surface gradually increases along the groove. An optical recording medium comprising: a group of cylinders moving to a land side and moving to a groove side within a decrease in radius, and formed by an envelope surface in contact with a side surface of the group of cylinders. 2. The optical recording medium according to claim 1, wherein the center of the bottom surface of the column group moves toward the land by 20 nm or more in addition to the increase in radius. When the width of a land where pits are not formed in advance is a normal land width a and the land width of a narrowest portion where a pit is formed in advance is a minimum land width b, (a-
The product of the pit width Wp represented by b) and the pit length Lp represented by the distance between two points where the tangent of the envelope surface and the inner periphery of the land intersect at the largest angle is 0.12 μm ^2. The optical recording medium according to claim 1, wherein the thickness is not less than 0.27 μm ² . 4. The optical recording medium according to claim 3, wherein said pit length Lp is 0.3 μm or more and 3.0 μm or less.