JPH09282716A - Optical information recording medium and optical recording/reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable beam tracking by forming a recording layer in such a manner that a groove width is larger than a land width and the reflectance of a recording mark part is higher than that before recording in the groove. SOLUTION: A groove 9 having a pitch of 1.0μm or lower and a land 10 narrower than the width of this groove 9 are alternately provided on a substrate. Since beam irregular reflection is large in the shoulder part of the narrow land 10 and the groove part 9 has more flat area, for beams 3, 4 and 5, 0-order diffracted beams from the groove part 9 are more intense than 0-order diffracted beams from the land 10. Thus, tracking is performed by moving all the three beams in the direction of the beam 5 if the 0-order diffracted beam intensity of the beam 3 is smaller than that of the beam 5 or in the direction of the beam 3 if it is larger. Further, a layer is formed such that the reflectance of a recording mark increases after recording, and thus, a tracking servo signal is made stable after recording. Therefore, even when a groove pitch is 1.0μm or lower, tracking is properly performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium and an optical recording / reproducing method, and more particularly to an optical recording by a three-beam tracking servo which operates stably even at a narrow track pitch of 1.0 μm or less. The present invention relates to an optical information recording medium suitable for a reproducing method.

[0002]

2. Description of the Related Art At present, C is a recordable medium that has a storage capacity of about 650 megabytes, which is the same as a CD (Compact Disc), and can be reproduced by an ordinary CD drive.
There is a D recordable disc (CD-R). CD
In order to maintain the compatibility of the tracking servo with the CD, -R records in a spiral groove portion that periodically meanders. Further, in order to make the servo and the reproduction signal compatible with each other, the groove width of the CD-R is narrower than the width between the grooves, and is designed so that the reflectance after recording is lower than that before recording. . CD-R has a track pitch of 1.6μ
The groove width is approximately 0.5 to 0.7 μm.
It is usually said that.

In recent years, progress has been made in the technology for increasing the density of optical discs. Particularly, in the case of read-only discs, there is a recording medium for moving image files having a CD size and a storage capacity of 3 to 5 gigabytes per side. Proposed (Nikkei Electronics, February 27, p.
p. 87-100 (1995)). It is considered that a recordable medium having the same storage capacity as the read-only disc and having compatibility with the CD-R will be needed sooner or later, and the development is currently underway. Even in such a medium, groove recording is considered to be performed from the viewpoint of tracking compatibility.

[0004]

Grooves and pit rows for recording are formed by first exposing and developing a glass master having a photoresist film, transferring this to a stamper, and then ejecting it. It is transferred to the substrate by molding or the 2P method. The exposure of the spiral or concentric grooves is performed by concentrating a laser such as an Ar gas laser on the master and exposing the master while rotating the master on a turntable and shifting the radial position with a linear motor. .

In recent years, the resolution of precision processing of photoresist has been greatly improved with the development of manufacturing technology for highly integrated semiconductors, but at present, the groove width that can be formed by Ar laser is 0.3 to 10. The lower limit is about 0.4 μm. Although it is possible to make the groove width narrower by exposure to ultraviolet rays, it is not preferable for the following reasons. That is,
Since it is difficult to keep the focused beam diameter of the semiconductor laser used for recording / reproducing in the drive at 1.0 μm or less for the time being, the width of the mark recorded in the groove is 0.3 to 0.5 μm.
The degree is the lower limit. It is often unfavorable to record marks by protruding from the groove, because leakage of signals to adjacent tracks, that is, crosstalk is increased.
Therefore, again, the groove width is preferably 0.3 to 0.4 μm or more.

Therefore, at present, the track pitch is 1.
When it is attempted to realize a narrow track pitch of 0 μm or less, particularly 0.6 to 0.8 μm, the groove width becomes wider than the width between the grooves. When the track pitch is narrower than 1.0 μm and the groove width is wider than the inter-groove width as described above, the tracking method that is widely used at present, that is, the push-pull method using the single beam, cannot obtain an error signal sufficiently and is stable. Hard to get a good tracking servo. In this case, the so-called three-beam method is suitable as the tracking method. The three-beam method itself can be realized using a known circuit configuration and an optical head (for example, "Optical Disc Technology" (supervised by Morio Onoue), Radio Technology Co. (1989)).

The three-beam method will be described with reference to the drawings.
FIG. 1 is a schematic diagram of an apparatus for performing 3-beam tracking, and FIG. 5 shows a case where 3-beam tracking is applied to an example of a conventional medium. In FIGS. 1 and 5, the beam emitted from the semiconductor laser 1 is divided into three beams by a diffraction grating 2 into a main beam 4 for signal recording / reproduction and sub-beams 3 and 5 for obtaining a tracking error signal. Optical disk 7 through splitter 6
Is irradiated. Light reflected from beams 3, 4, and 5, ie 0
The next-order diffracted light passes through the beam splitter 6 and reaches the three-divided photodiode 8.

In FIG. 5, grooves 9 and lands 10 wider than the grooves are alternately provided on the substrate, and recording marks 11 are provided in the grooves 9. In the present application, the groove means a concave portion on the substrate, and the land means a convex portion on the substrate. On the substrate, the main beam is arranged at the center of the groove 9 and the sub-beams are arranged at the front and rear thereof so as to deviate symmetrically from the groove center.

As shown in FIG. 5, when the groove width is narrower than the land width, the 0th-order diffracted light intensity of the sub-beams 3 and 5 is stronger when the beam is on the land than when it is in the groove. Therefore, for example, when tracking is deviated in the beam 3 direction, P3 (0th order diffracted light intensity of beam 3)
> P5 (0th order diffracted light intensity of beam 5). Therefore,
When P3> P5, the tracking servo is maintained so that the main beam 4 comes to the center of the groove by moving the three beams in parallel in the beam 5 direction and in the beam 3 direction if P3 <P5.

However, when a recording mark accompanied by a change in reflectance exists in the groove, particularly when a long mark such as a pit length recording exists, the diffracted light intensity of the sub beam is naturally affected. There is no problem when the reflectance of the recording mark is lower than that before recording. However, when the reflectance increases, the average reflectance in the groove increases, and the reflectance difference between the groove and the land decreases, which is not preferable. That is, even if the tracking is deviated from the groove center, the fluctuation of the 0th-order diffracted light amount of the sub beam becomes small, and it becomes difficult to obtain a normal tracking operation.

As described above, in the CD-R having a track pitch of 1.6 μm, the groove portion is narrower than the inter-groove portion, and the reflectance is lowered in the groove portion. Was required to decrease. More strictly, a certain limit is required for the value of the reflectance change at the mark. However, for a medium having a narrow track pitch and a groove width wider than the inter-groove width as described above, this premise is broken, and the three-beam method cannot be used as it is.

[0012]

The present inventors have arrived at the present invention as a result of extensive studies on a recording medium and a recording system which can maintain compatibility with a high density CD in the inter-groove recording. The gist of the present invention is an optical recording medium in which at least a recording layer is provided on a substrate provided with spiral or concentric circular grooves for tracking a light beam at a pitch of 1.0 μm or less. Wider than the width between the grooves,
The optical information recording medium is characterized by having a layer structure in which the reflectance of the recording mark portion becomes higher than the reflectance before recording when recording is performed in the groove. Another subject matter of the present invention is a method of recording / reproducing between grooves of the optical information recording medium, which is an optical recording / reproducing method characterized by performing a tracking servo by a three-beam method.

That is, the present photoresist exposure technique and the present recording laser beam diameter are used by making the groove width wider than the inter-groove width and providing a layer structure in which the reflectance is high at the mark portion after recording. At the same time, they have found that it is possible to provide a high-density recording medium suitable for tracking by the three-beam method and a recording / reproducing method thereof.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. In FIG. 2, grooves 9 and lands 10 having a width narrower than the grooves are alternately provided on the substrate, and recording marks 11 are provided in the grooves 9. In the present application, the groove means a concave portion on the substrate, and the land means a convex portion. Here, when recording is performed by making the groove width wider than the land width, that is, the inter-groove width, by narrowing the land width, it is possible to increase the density without the marks protruding from the groove. Easy to narrow. In this case, contrary to the conventional case, the diffuse reflection of the beam on the shoulder portion becomes large in the narrow land portion, and the flat portion becomes large in the groove portion, so that the beam 3, 4 and 5 are not reflected from the groove portion at the next time. The folding light is stronger than the 0th-order diffracted light from the land portion. Therefore, contrary to the case where the groove width is narrow, P3 (beam 3
(0th-order diffracted light intensity) <P5 (0th-order diffracted light intensity of beam 5) is moved in the beam 5 direction, and if P3> P5, 3 beams are moved in the beam 3 direction to perform tracking.

Furthermore, the tracking servo signal after recording becomes more stable by adopting a layer structure in which the reflectance of the recording mark increases after recording. On the other hand, in the case of a layer structure in which the reflectance decreases after recording, the average reflectance of the groove portion decreases, so the reflectance difference with the land portion becomes small, and tracking becomes difficult. With such a configuration, tracking can be suitably performed even when the groove pitch is 1.0 μm or less.

This medium has a tracking polarity opposite to that of the current medium, but by adding an inverting circuit for switching the polarity of the tracking error signal, the current medium and the medium relating to the present invention are in the same device. You can record and play with. The recording medium of the present invention may be a write-once medium, but may be a rewritable medium or a so-called light modulation overwritable medium. A preferred example of the present invention is a phase change type recording medium in which the above-mentioned recording layer detects a change in reflectance due to a phase transition between an amorphous state and a crystalline state. Is formed to record information.

Recording layer of overwritable phase change medium
Examples include various chalcogen-based alloys.
Of these, alloys containing Sb and Te as the main components are preferable.
In addition, in the present application, the main component is a specific atom in all atoms.
It means that the atomic ratio is 50 atomic% or more. here
Has a total amount of Sb and Te of 50 atomic% or more. Especially,
A_1-xM_x(0 ≦ x ≦ 0.9) {A is Sb_TwoTe_ThreeIntermetallic
Compound composition or Sb _0.7Te_0.3Near the eutectic composition (with Sb
Up to +30 atom% of Sb relative to the total amount of Te
Gap, and M is an element from group II to group VI}
The recording layer whose main component is the alloy
It is preferable because of its high reliability and less deterioration due to heat. example
For example, an alloy thin film containing Ge, Sb, and Te as main components
Or, if the main component is four elements of Ag, In, Sb, and Te.
Money is known. More specifically, GeTe and S
b_TwoTe_ThreeNear the pseudo-binary alloy, or AgIn
Te_TwoIt is known in the vicinity of the composition in which Sb is added to
JP-A-62-209742, JP-A-63-225934.
JP-A-5-151619 and JP-A-5-34547.
No. 8).

In the phase change medium using the above recording layer, overwrite recording is possible as follows. In order to erase the previously recorded recording mark, a beam having a bias power for heating the recording layer to a crystallization temperature or higher is irradiated, and the recording layer is formed only in a portion where a new amorphous recording mark is to be formed. The recording power for melting is superimposed. When the melted recording layer is cooled, an amorphous mark is formed if it is in a supercooled state.

In order to prevent deformation of the recording layer and the like due to repeated overwriting, perforation, and damage to the substrate, it is desirable that the overwritable phase change medium has a multi-layered structure. That is, a protective layer made of an inorganic compound, a phase change recording layer, a protective layer made of an inorganic compound, and a reflective layer made of a metal or a semiconductor are provided on a substrate. Furthermore, by providing a protective layer made of a photocurable or thermosetting resin on the reflective layer, it is possible to suppress deformation of the recording layer or the like,
It is effective in improving the scratch resistance of the medium. In the present application, these are collectively referred to as a recording layer configuration.

It is desirable that these protective layers are substantially transparent to the recording / reproducing light wavelength, and the light absorption of the protective layer is
It is desirable to suppress the incident light energy to less than 10%. The protective layer preferably has a melting point or a decomposition temperature sufficiently higher than the melting point of the recording layer. GeSb above
For Te-based or AgInSbTe-based recording layers,
The protective layer needs to be stable up to about 1000 ° C. A known material such as an inorganic compound, which is a highly heat-resistant dielectric, such as a metal or semiconductor oxide, nitride, carbide, fluoride, or sulfide can be used. More specifically, tantalum oxide, silicon oxide, yttrium oxide,
Examples thereof include silicon nitride, aluminum nitride, zinc sulfide, magnesium fluoride and the like. These dielectrics may be used alone or as a mixture. In particular, 10 to 4 for zinc sulfide
It is known that a protective layer in which 0 mol% of silicon oxide, yttrium oxide or the like is mixed has excellent durability against repeated overwriting (Japanese Patent Publication No. 4-74785).
JP-A-63-259855). Au, A for the reflective layer
It is preferable to use a high-reflectance metal such as g or Al or an alloy thereof, but other metals or semiconductors may be used for adjusting the thermal conductivity and the light absorption rate.

The above-mentioned recording layer structure can also be used to make the reflectance of an amorphous recording mark higher than that of the crystalline state. This is due to the multiple interference effect including the protective layer and the reflective layer. For example, in the GeSbTe-based recording layer, the protective layers above and below the recording layer are indispensable for increasing the amorphous reflectance.

Below, examples of calculation of reflectance and absorptance are also given.
Now, a preferred layer structure in the present invention will be described.
However, the present invention is limited to the following examples as long as the gist thereof is not exceeded.
It is not something to be done. Polycarbonate with a refractive index of 1.58
Lower protective layer, recording layer, upper protective layer, reflective layer on the substrate
The layers were laminated in this order. 20 nm thick Ge as a recording layer _Two
Sb_TwoTe_FiveAl alloy with a thickness of 100 nm for the film and reflective layer
A membrane was used. Where Ge_TwoSb_TwoTe_FiveComplex curvature of recording layer
The folding rate is 3.90-1.82i in the amorphous state, and in the crystalline state
3.73-3.81i, the complex refractive index of the Al alloy reflective layer is
1.77-5.48i. With upper and lower protective layers
With a refractive index of about 2.1, specifically ZnS
20 mol% SiO_TwoMixed with tantalum oxide
Was used.

Here, the optical constants such as the complex index of refraction used in the calculation are measured values at a wavelength of 680 nm, and the calculated values and the measured values are in good agreement. In this case, the wavelength 680
The calculation result of the protective layer thickness dependence of the reflectance in nm is shown in FIG. The lower protective layer thickness is plotted on the horizontal axis and the reflectance is plotted on the vertical axis, and the upper protective layer thickness x is changed. The reflectances in the crystalline state and the amorphous state are shown by Rc and Ra, respectively. When the thickness of the upper protective layer is 80 nm, the thickness of the lower protective layer is 0.
At ~ 90 nm and 150-250 nm,
It can be seen that in the range of the upper protective layer thickness of 100 to 120 nm, the reflectance of the amorphous mark can be higher than the crystalline state before recording in the total thickness of the lower protective layer, which is preferable.

These film thickness dependences are due to wavelengths of 600 to 70.
It may be considered that the above condition is satisfied almost as it is in the range of 0 nm. This is because the optical constant hardly changes in the wavelength range of 600 to 700 nm, and the measured value at 680 nm can be applied as it is, and (1 / wavelength)
Is substantially proportional to the wavelength of 600 to 700 nm
This is because there is no great change in the range of.

The thickness of the protective layer is equivalent to the wavelength, that is, (wavelength / 2 with respect to the refractive index n of the protective layer.
The film thickness difference of n) has an optically equivalent effect.
FIG. 4 shows the calculation result of the protective layer thickness dependency of the ratio of the light absorptance of the recording layer in the crystalline / amorphous state. The lower protective layer film thickness is plotted on the horizontal axis and the light absorption ratio Ac / Aa is plotted on the vertical axis, and the upper protective layer film thickness x is changed. Ac and Aa are values in which the light absorptance of the recording layer in the crystalline state and the amorphous state is represented with the incident light intensity of 1.0. FIG.
In the layer structure in which Ra is smaller than Rc in FIG.
Ac / Aa is approximately 1.0, but Ra is Rc in FIG.
In the larger layer structure, Ac / Aa> 1.
It is 0.

It is generally known that the phase change type recording medium satisfying Ac / Aa> 1.0 has a remarkable advantage when one-beam overwrite is performed at a high linear velocity of several m / sec or more. (S. Ohkubo et al., Jpn. J. App.
l. Phys. 32 (1993), p. 5230, or Kitaura et al., Proceedings of the 6th Phase Change Record Study Group, p.
59). Therefore, when the reflectance in the amorphous state is higher than the reflectance in the crystalline state, Ac / Aa> almost always>
Since it is 1.0, the additional effect of improving the recording characteristics at high linear velocity can be obtained, which is more preferable.

Further, in FIG. 4, the film thickness of the upper protective layer is 10
It can be seen that in the range of 0 to 120 nm, Ac / Aa> 1.3 over a wide range of the lower protective layer film thickness.
It is also known that in the case of a medium satisfying Ac / Aa> 1.3, the effect of improving the erasing ratio at a high linear velocity is particularly remarkable (Takeguchi et al., 6th Phase Change Recording Workshop, p. .64), particularly preferred.

Another preferable example of the present invention is a phase change type recording medium in which the recording layer detects a change in reflectance due to a phase transition between an amorphous state and a crystalline state. As described above, a crystal mark is formed to record information. For example, as a write-once medium, this type is preferable because it is easy to obtain a structure in which the reflectance of a recording mark is high in a single layer and an initialization operation after film formation is not required.

The recording layer that can be used for this is, for example,
Ge and I are added to a system containing two elements of Sb and Sn as main components.
Known thin films such as alloy thin films to which at least one kind of a third element such as n, Zn, Al, Ag, Pd, Au, Si, and Bi is added are known (US Pat. No. 4,795,695, 4).
798785, 4812385, 4981722). The amount of the third element added is preferably about 5 to 20 atom%. In particular, a recording medium containing SbSnIn as a main component has a stable amorphous state and is crystallized at a high speed by irradiation with a light beam, and is therefore preferable as a highly sensitive and highly reliable disc (US Pat. No. 4,960,680).
issue).

[0030]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Track pitch 0.
75 μm, groove width 0.5 μm, land width 0.25 μm
m, the depth of the groove is 50 nm, and the (ZnS) ₈₀ (SiO ₂ ) _80
A protective layer composed of a ₂₀ (mol%) mixed film is formed at 110 nm, I
20nm recording layer composed of _{n 1 0 Sb 65 Sn 25,} 20nm protective layer of tantalum oxide, to prepare a medium having 100nm a reflective layer of Al _97.5 Ta _2.5 alloy. This medium is a write-once type medium for performing crystallization recording on an amorphous medium. The groove shape is obtained by performing AFM observation and deriving the groove width and the land width at the midpoint of the groove depth.

Three-beam tracking servo characteristic evaluation at a wavelength of 635 nm was performed on this medium. However, since a recording / reproducing apparatus with a wavelength of 635 nm cannot currently obtain high power used for recording, recording with a wavelength of 680 n is required.
m recording / reproducing apparatus. First, wavelength 680n
Crystallization recording was performed at a linear velocity of 3 m / s by using a recording / reproducing device that performs push-pull type tracking servo with NA of 0.6 m. The recording power was 5 mW and the reproducing power and the bias power for tracking were 0.8 mW. The recording method is EFM modulation recording in which the shortest mark length is 0.6 μm. As a result, the reflectance in the amorphous state before recording is 20.
%, But it increased to 45% due to crystallization recording.

Next, this medium was changed to a wavelength of 635 nm and NA.
When a recording / reproducing apparatus for performing a 3-beam tracking servo of 0.6 was used to reproduce with a beam having a reproduction power of 1 mW, stable tracking servo was obtained. 63
The reflectance before recording in the 5 nm drive was 15%, and the reflectance after recording was 40%.

[0033]

The optical information recording medium of the present invention can be easily grooved even at a narrow track pitch, and it has been difficult to apply the conventional three-beam method tracking servo.
Three-beam tracking can be stably performed even on a recording medium having a layer structure in which the reflectance increases after recording, and stable tracking servo can be obtained before and after recording.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an example of an apparatus used in the method of the present invention.

FIG. 2 is a schematic explanatory view of an example of a medium of the present invention.

FIG. 3 is a graph showing an example of the relationship between reflectance and protective layer film thickness.

FIG. 4 is a graph showing an example of the relationship between the light absorption rate and the protective layer film thickness.

FIG. 5 is a schematic explanatory view of an example of a conventional medium.

[Explanation of symbols]

 1 semiconductor laser 2 diffraction grating 3 sub-beam 4 main beam 5 sub-beam 6 beam splitter 7 optical disk 8 3-division photodiode 9 groove 10 land 11 recording mark

Claims (10)

[Claims] 1. An optical recording medium in which at least a recording layer is provided on a substrate provided with spiral or concentric circular grooves for tracking a light beam at a pitch of 1.0 μm or less, and the groove width is a groove. The optical information recording medium is characterized in that the recording layer has a width larger than the gap and the reflectance of the recording mark portion in the groove is higher than that before recording. 2. A recording layer is a phase change type recording medium for detecting a change in reflectance due to a phase transition between an amorphous state and a crystalline state, and an amorphous recording mark is formed with the crystalline state as an initial state. The optical information recording medium according to claim 1, wherein the information is recorded by performing the recording. 3. The optical information recording medium according to claim 2, wherein the recording layer is an alloy containing Sb and Te as main components. 4. The recording layer is A _1-x M _x (0 ≦ x ≦ 0.9)
{A is the composition of Sb ₂ Te ₃ intermetallic compound or Sb _0.7 T
e _0.3 Near a eutectic composition (including a deviation of up to +30 atomic% in the amount of Sb with respect to the total amount of Sb and Te), and M is an alloy represented by Group II to Group VI} The optical information recording medium according to claim 3, wherein 5. A protective layer made of an inorganic compound on a substrate,
5. The optical information recording medium according to claim 2, further comprising a phase-change recording layer, a protective layer made of an inorganic compound, and a reflective layer made of a metal or a semiconductor or an alloy thereof. . 6. The light absorption rate Ac in the crystalline state is higher than the light absorption rate Aa in the amorphous state.
The optical information recording medium according to the above. 7. The optical information recording medium according to claim 6, wherein Ac / Aa> 1.3. 8. A recording layer is a phase change type recording medium that detects a change in reflectance due to a phase transition between an amorphous state and a crystalline state, and a crystalline recording mark is formed with the amorphous state as an initial state. The optical information recording medium according to claim 1, wherein the information is recorded by performing the recording. 9. The optical information recording medium according to claim 8, wherein the recording layer is an alloy thin film containing Sb and Sn as main components. 10. A method for recording / reproducing on / from the optical information recording medium according to claim 1, wherein the tracking servo is performed by a three-beam method.