JPH1021583A - Optical recording medium, and recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain equivalent high signal quality whichever a land or a groove is recorded and durability against over-write repetition, by using both the groove and the land as a recording area. SOLUTION: A lower dielectric protective layer, a phase transition type recording layer 2, an upper dielectric protective layer and a metal reflecting layer are layered in order on a transparent substrate 1 having formed grooves, and both the groove and the land are used as recording area, which is irradiated with a laser light having a wavelength of <=700nm so as to record, erase and reproduce information. Then, a phase difference α between reflecting light from nonrecorded area and reflecting light from a recorded area is satisfied with (m-0.1)π<=α<=(m+0.1)π. Then, a groove width GW, a land width LW and a groove depth (d) are satisfied with 0.3μm<=GW<=0.8μm, 0.3μm<=LW<=0.8μm, 0.62×(λ/NA)<=LW<=0.8×(λ/NA), (GW+LW)/2>0.6×(λ/NA) and λ/7n<d<λ/5n, where (n) is a reflective index of the substrate and NA is a numerical aperture of a focusing lens.

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 a recording / reproducing method, and more particularly, to an optical recording medium for recording, reproducing and erasing information in both a groove and a groove of a substrate by irradiating a laser beam. The present invention relates to an information recording medium and a recording / reproducing method using the same.

[0002]

2. Description of the Related Art In recent years, as the amount of information has increased, there has been a demand for a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed. However, an optical disk is expected to exactly meet such a use. I have. Such demands for higher capacity and higher density of recording media are inevitable in the era of imposing on recording media and recording devices in handling enormous amounts of image information and audio signals. The progress is in tandem with progress.

[0003] As a specific means for increasing the density, in an optical disk, a wavelength of a light source is shortened and a high NA (N
MCAV (Merical Aperture) to reduce the convergent beam diameter of the irradiation light, shorten the recording mark length, increase the recording frequency toward the outer circumference under a constant rotation speed, and keep the recording density at the inner and outer circumferences constant. Modified Constant Angular Velocit
y), mark edge recording, which puts information at the start and end of the mark, has been developed and used, and a method for further densification is being sought for the future.

In a recordable optical disk, a guide groove is previously formed on the disk to form a so-called track. Normally, information signals are recorded and collected by condensing laser light between or within the guide grooves.
Playback or erasure is performed. In general optical disks currently on the market, information signals are usually recorded only between the guide grooves or inside the guide grooves, and the other is a boundary for separating adjacent tracks to prevent signal leakage. It just plays a role.

[0005] If it is possible to record information in this boundary portion, for example, in the guide groove when recording between the guide grooves, and between the guide grooves when recording in the guide groove, if it is possible to similarly record information. The recording density is doubled, and a large improvement in the recording capacity can be expected. Hereinafter, a method of recording information on the guide groove in the groove, a land between the guide grooves, and information on both the land and the groove is abbreviated as L & G recording.

[0006] As a proposal for L & G recording,
No. 57859, but when such a technique is used, great care must be taken to reduce crosstalk. That is, in the L & G recording described in Japanese Patent Publication No. 63-57859, the interval between the recording mark row of a certain track and the recording mark row of a track adjacent thereto is half of the convergent beam diameter. The convergent beam is irradiated to the adjacent recording mark row.

For this reason, there is a problem that the crosstalk during reproduction is increased and the reproduction S / N is deteriorated. In order to reduce the crosstalk, for example, there is a method of reducing the crosstalk by providing a special optical system and a crosstalk cancel circuit in an optical disk reproducing device. (SPI
E Vol. 1316, Optical Data
Storage (1990) pp. 35)

However, this method has a disadvantage that the optical system and the signal processing system of the apparatus become more complicated. As a method of reducing crosstalk without specially installing a special optical system or signal processing circuit to reduce reproduction crosstalk, the width of grooves and lands is made equal, and the groove depth is adjusted to the reproduction light wavelength. There is a proposal that it is effective to set it within a certain range. (J
pn. J. Appl. Phys. Vol 32 (199
3) pp. 5324-5328).

According to this, the crosstalk is reduced when the land width is equal to the groove width and the groove depth is λ / 7n to λ / 5n (λ: reproduction light wavelength, n: refractive index of the substrate). Are shown as calculations and experimental facts.
This is also described in JP-A-5-282705. However, although the effect of reducing crosstalk can be obtained by setting the groove depth to an optimum value, the CN ratio between the land and the groove is unbalanced.

When performing L & G recording, there is a difference between the carrier level (signal quality) of the land and the carrier level of the groove, and as a result, a significant decrease in the CN ratio of one of the discs is desirable in the signal quality of the disk. Absent.

On the other hand, when the track pitch is reduced for high density, it is usually sufficient to select the track pitch and groove shape so that the amount of crosstalk is equal to or less than a predetermined level. There is another problem that needs to be considered. That is, when a certain track is repeatedly overwritten, an amorphous bit in an adjacent track disappears, that is, recrystallization occurs. Although the reason is not necessarily clear, when recording on an adjacent track, the temperature of the track is raised by the weak laser light at the foot of the focused light beam intensity distribution, and the temperature of the amorphous bit portion is heated to a temperature higher than the crystallization temperature. It is thought that it is.

Although the time is several hundred nanoseconds at a time, it is gradually recrystallized during repeated heating. For example, there may be a case where the CN ratio of an adjacent track is reduced from 55 dB in the initial stage to less than 50 dB in 10,000 repeated overwrites. This problem is hereinafter referred to as cross-erase. In the phase change medium, attention must be paid to the minimum track pitch due to cross-erase, rather than the optical diffraction limit, but the limit is not always clear.

Further, when the density is increased by narrowing the track pitch while keeping the width of the groove and the land at 1: 1, the remaining mark of the previous mark after repeated overwriting and the deterioration of the jitter of the recording mark are deteriorated. It was found that the characteristics were significantly deteriorated in the land.

[0014]

SUMMARY OF THE INVENTION The present invention solves this problem. In particular, in an L & G recording type optical disc using a laser beam having a wavelength of 700 nm or less as a light source, the carrier level of the land and groove recording marks is reduced. It is an object of the present invention to provide a high-density optical disk which can eliminate the balance and can obtain the same high signal quality and the durability against repeated overwriting even when recording is performed on either a land or a groove.

[0015]

SUMMARY OF THE INVENTION The present invention has been made as a result of repeatedly examining the phase difference of reflected light from an unrecorded area and a recorded mark and the shapes of lands and grooves. A lower dielectric protection layer, a phase change recording layer, an upper dielectric protection layer, and a metal reflection layer are sequentially laminated on the transparent substrate thus formed. An optical recording medium for recording, erasing, and reproducing information by irradiating a laser beam having the following wavelength, wherein (1) reflected light from an unrecorded area and reflected light from a recorded area defined below. The phase difference α α = (phase of reflected light from unrecorded area) − (phase of reflected light from recorded area) satisfies the following equation:

[0016]

(M−0.1) π ≦ α ≦ (m + 0.1) π (m is an integer)

(2) Groove width GW, width LW between grooves, groove depth d
Satisfies the following equation

[0018]

## EQU9 ## 0.3 μm ≦ GW ≦ 0.8 μm

[0019]

## EQU10 ## 0.3 μm ≦ LW ≦ 0.8 μm

[0020]

0.62 × (λ / NA) ≦ LW ≦
0.8 × (λ / NA)

[0021]

(GW + LW) / 2> 0.6 × (λ / N
A)

[0022]

Λ / 7n <d <λ / 5n (where λ: wavelength of irradiation light, n: refractive index of substrate, N
A: numerical aperture of a focusing lens).

Further, using such an optical recording medium, both the groove and the groove are used as recording areas, and 700 n
A recording / reproducing method characterized in that recording, erasing, and reproducing are performed by one-beam overwriting of a laser having a wavelength of m or less.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the optical disk of the present invention having the above-described structure, the carrier level of a recording mark becomes the same regardless of whether data is recorded on a land or a groove, and the durability of the land against repeated overwriting is enhanced. These have a wavelength of 700 n in order to perform high density recording.
This is an essential rule in assuring the reliability of an L & G recording type optical disk that uses a laser beam of m or less as a light source.

Next, how the present invention acts on the reproduction process of the optical recording medium for land and groove recording to produce an effect will be described in detail by using a simple model on the basis of the effect. FIGS. 1 to 4 are schematic diagrams showing a case where a reproduction light beam is irradiated on a land or a groove of an L & G recording optical disk. Layers other than the recording layer 2 are omitted for easy viewing of the drawing. The reproducing convergence beam 5 is condensed using an objective lens or the like, and is irradiated onto the recording layer 2 from the substrate 1 side. Assuming that the width of the land 3 is equal to the width of the groove 4 and half the beam diameter, a step (groove depth) between the land 3 and the groove 4 is d.

Here, the unrecorded recording layer has a crystalline state,
The recording layer during recording is in an amorphous state. The intensity of the convergent beam 5 is a Gaussian distribution according to an actual model, and is within a range of 1 / e ² (e is the base of natural logarithm) of the center intensity.
That is, 0.82 (λ / NA) is defined as the beam diameter (λ is the wavelength of the convergent beam 5, and NA is the numerical aperture of the focusing lens). 1 and 3 show the case where the convergent beam 5 exists in the unrecorded area, and FIGS. 2 and 4 show the case where the convergent beam 5 exists on the recording mark 8. It is assumed that the recording mark 8 is sufficiently longer than the convergent beam 5 to simplify the calculation. As will be shown later in the embodiment, there is no problem even if the recording mark is actually shorter than the convergent beam diameter.

Since the convergent beam 5 is emitted from the substrate 1 side, it is incident and reflected from the other side of the drawing. Therefore, when viewed from the light source side, the land 3 is concave, and conversely, the groove 4 is convex. When the surface of the groove 4 is used as a reference for the phase, the phase of the reflected light from the land 3 is delayed by 2π · 2nd / λ (n is the refractive index of the substrate 1 and λ is the convergent beam 5).
Wavelength).

The phase change is not caused only by the groove depth, but generally the phase difference is also changed by the change of the optical constant before and after the phase change of the recording layer. here,
It is defined that the phase of the reflected light from the amorphous region is delayed by 2πα (α: phase difference) from the reflected light from the crystalline region. Hereinafter, the amplitude reflectance of the convergent beam will be formulated using the phase difference α as necessary, using the groove surface as a reference for the phase.

The amount of reflected light from the center of the convergent beam 5 applied to the crystal region is R _c1 , the amount of reflected light from both ends is R _c2 , and the amount of reflected light from the center of the convergent beam 5 applied to the amorphous region is R _c1 . R _a1 , the amount of light reflected from both ends is R
_a2 . Since land width = groove width, this is applicable when the beam center is at either the land or the groove. Amplitude reflectance phi ₁ when there is a convergent beam 5 on the land 3 with no amorphous recording mark as shown in Figure 1 can be expressed by the following equation. Note that i is an imaginary unit.

[0030]

Φ ₁ = R _c1 · exp [−2πi · 2nd / λ] + R _c2 · exp [−2πi · 0] (a) where R _c1 is a land area 6 irradiated with a convergent beam.
R _c2 is the amount of reflected light from the groove area 7 irradiated with the convergent beam.

As shown in FIG. 2, the amplitude reflectance φ ₂ when the convergent beam 5 is located on the land where the amorphous recording mark 8 is located
Can be expressed by the following equation.

[0032]

Φ ₂ = R _a1 · exp [−2πi · (2nd / λ + α)] + R _c2 · exp [−2πi · 0] (b) where R _a1 is a land area 6 irradiated with a convergent beam.
R _c2 is the amount of reflected light from the groove area 7 irradiated with the convergent beam.

As shown in FIG. 3, when the converging beam 5 is present in the groove 4 having no amorphous recording mark, the amplitude reflectance φ
₃ can be represented by the following equation.

[0034]

Φ ₃ = R _c1 · exp [−2πi · 0] + R _c2 · exp [–2πi · 2nd / λ] (c) where R _c1 is the reflection from the groove area 7 irradiated with the convergent beam. The amount of light, _Rc2, is the amount of light reflected from the land area 6 irradiated with the convergent beam.

As shown in FIG. 4, the amplitude reflectance φ when the converging beam 5 is located in the groove where the amorphous recording mark 8 is located
₄ can be represented by the following equation.

[0036]

Φ ₄ = R _a1 · exp [−2πi · α] + R _c2 · exp [-2πi · 2nd / λ] (d) where R _a1 is the reflection from the groove region 7 irradiated with the convergent beam. The amount of light, _Rc2, is the amount of light reflected from the land area 6 irradiated with the convergent beam. here,

[0037]

R _c2 = βR _c1 (e)

[0038]

[Equation 19] R_a2= ΒR_a1 (F) (where 0 <β <1). R_c= R
_c1+ R_c2, R_a= R_a1+ R _a2Equation (e) and equation
Arranging (f),

[0039]

R _c1 = R _c / (1 + β) (g)

[0040]

R _c2 = βR _c / (1 + β) (h)

[0041]

R _a1 = R _a / (1 + β) (i)

[0042]

R _a2 = βR _a / (1 + β) (j) Substituting equations (g) to (j) into equations (a) to (d) and rearranging,

[0043]

Φ ₁ = [R _c / (1 + β)] [β + exp [-4πind / λ]] (k)

[0044]

Φ ₂ = [1 / (1 + β)] · [βR _c + _Ra · exp [-4πind / λ−2πiα]] (1)

[0045]

[Formula 26] φ ₃ = [R _c / (1 + β)] · [1 + β · exp [−4ind / λ]] (m)

[0046]

Equation 27] _{φ 4 = [1 / (1} + β)] · [R a · exp [-2πiα] + βR c · exp [-4πind / λ]] (n) where, in the case of recording on the land reproduced carrier level C
L '(L) is

[0047]

(28) CL ′ (L) = | φ ₁ | ² − | φ ₂ | ² (o) Similarly, the reproduction carrier level CL '(G) when recorded in a groove is

[0048]

(29) is proportional to CL ′ (G) = | φ ₃ | ²⁻ | φ ₄ | ² (p).

No difference in carrier level between the land and the groove means that the difference between the equations (o) and (p) is zero.
It is nothing but becoming. The difference is calculated by substituting the expressions (k) to (n) into the expressions (o) and (p), and the difference is 0
Finding the necessary conditions

[0050]

Α = mπ (where m is an integer) (q) The phase difference α does not necessarily have to be exactly mπ, but is effective as long as the disc reflectance is within the range of ± 0.1π.

If the phase difference is (m-0.
1) When it is less than π, it is bad that the carrier level of the land becomes significantly smaller than that of the groove. On the other hand, when the phase difference exceeds (m + 0.1) π, the carrier level of the groove is poor. However, it is a bad point that is significantly smaller than the land.

Thus, the phase difference α is set to (m ± 0.1) π
Within this range, high signal quality can be assured even when recording on either land or groove tracks, and the range of phase difference between phase transitions required for this is determined by the optical constant and film thickness of each layer. Can be realized by appropriately selecting.

Next, the groove shape of the present invention will be described in detail. First, a method for measuring the groove width and the groove depth will be described.
The measurement was performed by irradiating He-Ne laser light (wavelength: 630 nm) from the side of the substrate having no groove, and diffracting the transmitted light by the groove of the substrate with the zero-order light intensity I ₀ , the first-order light intensity I ₁ ,
This is performed by measuring the secondary light intensity I ₂ and the angle of the diffracted light. P is the groove pitch (groove pitch), w is the groove width,
When d is the groove depth (groove depth), n is the refractive index of the substrate, λ is the laser wavelength, θ is the angle between the 0th order light and the 1st order light, and when the groove is rectangular,

[0054]

P = λ / sin θ Also,

[0055]

Ε = w / P, δ = 2 (n−1) πd / λ,

[0056]

[Expression 33] I ₂ / I ₁ = cos ² (πε)

[0057]

I ₁ / I ₀ = ｛ ² sin ² (πε) (1-cos
δ)｝ / [π ² ｛1-2ε (1-ε) (1-cos
δ)｝]

Since the above relationship holds, the groove width and groove depth can be calculated. Although the actual groove shape is not a perfect rectangle, in the present invention, the groove shape uses a value in which the width and the depth of the groove are uniquely determined by the above-described measuring method. Therefore, the actual groove shape may deviate from the rectangle.

The width of the land and the groove is 0.3-0.
It needs to be in the range of 8 μm. If the land and groove widths are smaller than 0.3 μm, stable tracking cannot be obtained, and manufacturing is difficult with current cutting techniques. Also, if it is wider than 0.8 μm,
The purpose of increasing the recording density cannot be achieved.

As described above, the groove depth of the substrate must be in this range because the crosstalk from the adjacent track is reduced when the groove depth is λ / 7n to λ / 5n. It is.

After good initial characteristics can be obtained in both the land and the groove as described above,
It is necessary to further improve the durability against repeated overwriting and the durability against the cross erase described above. According to the study by the present inventors, the repeated overwrite durability of the groove was better when the groove width was smaller. Of course, it is necessary that the recording mark does not protrude from the groove. This is described, for example, in JP-A-6-33806.
No. 4 has a description relating to the convergent beam shape. However,
No mention is made that the repeated overwrite durability is affected by the groove width or land width.

On the other hand, it has been found that the repetitive overwrite durability of the land depends on the relative relationship between the land width and the beam diameter. When the land width becomes smaller than a specific value with respect to the beam diameter, it is found that the land rapidly deteriorates.

That is, when the land width is 0.62 × (λ / N
Within the range from A) to 0.8 × (λ / NA), there is no erasure of the previous mark and no remarkable deterioration of the jitter of the recording mark when repeated overwriting is performed, and the characteristics are the same as those when recording on the groove. Is kept. If the land width is smaller than this, when the recording mark is repeatedly overwritten on the land, the erasure of the previous mark becomes remarkable, and the jitter of the recording mark is remarkably deteriorated. If the land width is larger than this, there is no problem with the repetitive overwrite characteristics of the land, and good characteristics can be obtained.However, from the viewpoint of high-density recording, it is ineffective to widen the land width and lower the recording density. Not a good idea.

Further, it has been found that the cross erase phenomenon also depends on the relative relationship between the beam spot diameter and the recording track pitch. That is, there is a minimum track pitch that can reduce the cross erase to a practically negligible level, which depends only on the beam spot diameter.

L & G recording groove pitch (GW + L)
W) is greater than 1.2 (λ / NA), that is, L &
Substantial track pitch of G recording ｛(GW + LW) /
If the 2} larger and than 0.6 (λ / NA), can prevent signal degradation of the adjacent track by cross erase, 10 ⁴
The decrease in the CN ratio after repeated overwriting can be suppressed to less than 3 dB, which is a level having no practical problem.

The theoretical meaning will be discussed below.
FIG. 5 is a schematic diagram showing the shape of the convergent beam. The convergent beam 9 passing through the focusing lens 12 has an intensity distribution 10 having a main peak and a sub-peak. The diameter of the central spot, which is the main peak, is represented by approximately 1.2 (λ / NA). Airy disk (airy disk) 1
One. The value of 0.6 (λ / NA) theoretically corresponds to exactly half of the Airy disk 11. From this, it is considered that the cross-erase phenomenon has, as a first approximation, a physical meaning that an adjacent track is heated by a weak laser beam of the convergent beam 9 at the foot of the Airy disk 11.

By the way, the currently known GeSbT
e, AgInSbTe, InSnTe, InSbTe, etc.
The phase change recording layer containing at least 40 at% as a main component of any of IIIb, IVb, Vb and VIb group elements or a mixture (alloy) thereof has a thermal conductivity of two to three orders of magnitude compared to a magneto-optical recording layer or the like. It is a small order. In addition, heat insulation is substantially performed in the order of 10 to 100 nanoseconds required for recording. Therefore, the cross erase phenomenon is hardly affected by the heat conduction of the phase change type recording layer. Therefore, the minimum track pitch is substantially determined only by the beam spot diameter, and thus the light beam wavelength and NA.

[0068] However, the reduction of the cross erase in repetitive overwriting 10 ⁴ times or more, although limited in layer structure and the recording layer properties of the recording medium is slightly is effective. Among the alloy recording layers described above, in the composition in which reversible change between crystal and amorphous is possible and cross erase is small, the melting point Tm
Is less than 700 ° C. and the crystallization temperature Tg is 150 ° C. or more in many cases.

If the Tg is lower than 150 ° C., the stability of the amorphous state is poor and cross-erasing is likely to occur. On the other hand, when Tm is 700 ° C. or higher, the energy to be irradiated at the time of recording becomes high, and cross erase is likely to occur in an adjacent track. In fact, Ge ₁ Sb ₂ Te ₄ or Ge ₂ Sb ₂ T
In e ₅ near composition, Tm is from 600 to 620 ° C., Tg is 1
50-170 ° C. Ag ₁₁ In ₁₁ Te ₂₃ Sb
_{In the case of 55} , Tm is about 550 ° C. and Tg is about 230 ° C.
In general, when the thickness of the recording layer exceeds 30 nm, the recording sensitivity is lowered, and heat is easily released to an adjacent track at the time of recording.

An important parameter related to the melting of the phase-change recording layer when forming the amorphous recording mark is the light absorption of the recording layer. In terms of obtaining a high carrier level in any track of the land or the groove, the effect is further amplified by specifying the ratio of the light absorption rate of the recording layer before and after the phase change to a certain range.

As a feature of the phase change type optical disk,
One-beam overwrite as described in -32811 and the like. In the PWM recording, information of 0 or 1 is assigned to the front end and the rear end of the recording mark, so that it is particularly required that the shape of the front end and the rear end of the mark is not distorted at the time of recording. However, with one-beam overwriting, the recording mark becomes distorted because the heating and cooling processes become uneven due to differences in thermal conductivity depending on whether the recording layer before recording is in an amorphous state or a crystalline state. Has been pointed out. Further, as described in, for example, Japanese Patent Application Laid-Open No. 5-298747, when the light absorption in the crystalline state is larger than the light absorption in the amorphous state, a larger CN is obtained.
Ratio, high erasure rate and wide power allowance (margin)
There is a proposal that you can get.

However, according to the study by the present inventors,
If the light absorptance in the crystalline state is
Light absorption in the crystalline state
A rate _c, The light absorption coefficient of the amorphous state is A_aAnd when
Ratio A_c/ A_aBut,

[0073]

Equation 35 The disk designed a layer structure of the disk to be in the range of _{0.84 ≦ A c / A a <} 1.01, jitter CN ratio or recording marks have been found to be particularly excellent. This is not limited to the case where the rotational speed of the disk is within a specific narrow range, but the linear velocity is 1.4 m / s.
The effect was remarkably observed over a wide range from to 15 m / s.

If A _c / A _a is less than 0.84, an imbalance occurs in the temperature rise / fall process during melting of the recording layer during overwriting due to the presence or absence of a recording mark existing on the recording track. The distortion of the mark shape becomes a problem. On the other hand, if the initial state (non-recorded state) of the disk is high and the recorded state is low, the recording sensitivity tends to be lower at less than 0.84. 84 or more is desirable.

In consideration of sensitivity and stability, the metal reflection layer is preferably made of an alloy of Al and Ti or Al and Ta. The content of Ti or Ta is 0.5 at%.
To 3.5 at%. At this time, the loss of the reflectance of the disk is small, and the disk can easily function as an appropriate heat dissipation layer.

Known methods can be used for forming these thin films, such as a method of forming a normal optical thin film such as magnetron DC sputtering or RF sputtering on a substrate disk of resin or glass in which grooves are formed in advance. . It is desirable to form a resin layer on the metal reflective layer by coating or spin coating to protect the film.

Various combinations are possible for the dielectric used for the protective layer, and the dielectric is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, Mg, Ca, Sr, Y, L, which have high transparency and high melting point
a, Ce, Ho, Er, Yb, Ti, Zr, Hf, V,
Oxides such as Nb, Ta, Zn, Al, Si, Ge, and Pb, sulfides, nitrides, and fluorides such as Ca, Mg, and Li can be used.

Of these, ZnS and SiO ₂ or Y ₂ O
_{In the} case of using at least one mixed film of ₃ , the content of SiO ₂ or Y ₂ O ₃ is preferably 5 to 40 mol% because the storage stability of the recorded disk is excellent.

In designing the disk of the present invention, it is necessary to accurately grasp the phase difference of the reflected light before and after the phase change. The phase difference can be measured by a laser interference microscope or the like. Further, it is more desirable that the value of A _c / A _a be accurately grasped and set within a specific range from the viewpoint of improving the CN ratio and reducing the jitter of the recording mark. Since A _c / A _a is the absorptance ratio of only the recording layer in the multilayer structure, it cannot be known by direct measurement. However, both the phase difference of the reflected light before and after the phase change and the absorptance ratio A _c / A _a can be obtained by calculation using the optical constant and the film thickness of each layer (the calculation method is “Basic and Method of Spectroscopy” (Kudo) Keie, Ohmsha, 1985) Chapter 3). The calculated values of the phase difference and the absorptance ratio in the present invention were calculated based on the method described in this document.
The optical constant of each layer may be measured in advance by preparing a single-layer film by a method such as sputtering and using an ellipsometer.

For recording / erasing / reproducing of the optical disk of the present invention, a one-beam laser condensed by an objective lens is used, and irradiation is performed from the substrate side of the rotating optical disk. At the time of recording and erasing, a rotating disk is irradiated with a pulse-modulated laser beam to change the recording layer into two reversible states, a crystalline state or an amorphous state, and a recording state or an erasing state (unrecorded state). I do. At this time, it is also possible to simultaneously erase (overwrite) marks existing before recording while recording.

At the time of reproduction, the rotating disk is irradiated with a laser beam having a lower power than the laser power at the time of recording and erasing, and the intensity change of the reflected light is detected by a photodetector to determine the recorded or unrecorded state. At this time, the phase state of the recording layer immediately before reproduction must not be changed.

The wavelength of the laser beam used for recording and reproduction must be 700 nm or less in order to realize high-density recording. Considering the ultraviolet absorption of the disk substrate, 3
00 nm or more is preferable. As the laser light, for example, A
lGaAs, AlGaAsP, AlGaInP, GaN
500-70 output from a III-V semiconductor laser such as
0 nm laser light, Ar, Kr, He-Cd, He-N
laser light of 400 to 650 nm output by a gas laser such as e, ZnCdSe, ZnSe, ZnCdS, ZnS
400-5 output from II-VI semiconductor lasers such as eS
A laser beam of 00 nm and a group III-V semiconductor laser output beam can be obtained through an SHG (second harmonic generation) element.
Laser light of 0 to 390 nm, Y excited by a semiconductor laser
350 nm laser light obtained by outputting the AG laser output light through a THG (third harmonic generation) element. Considering the miniaturization of the optical disk system, the laser light of the semiconductor laser is preferable.

In order to reduce the leakage of the signal from the adjacent track to both the groove and the land, it is desirable that the groove width and the land width be 1: 1. However, in order to secure the track cross signal or to prevent deterioration of the characteristics when performing repeated recording and erasing many times, crosstalk may occur due to the optimal shape of the land and groove. It may be intentionally slightly deviated from 1: 1 within a range that does not exist.

The disk of the present invention can be used as a single-plate disk using only one surface, or can be made into a double-sided disk by laminating two disks with the surface opposite to the substrate facing each other. Even in the case of a double-sided disk, by using a drive having a structure in which optical pickups are arranged on both sides of the disk, it is possible to simultaneously perform recording, erasing and reproduction on both sides without replacing the disk surface.
This is an important feature not found in a magneto-optical disk that requires a magnet on the side opposite to the laser beam irradiation side.

The optical disc for L & G recording of the present invention is a rewritable optical information recording medium,
It can also be used as a write-once type that can be recorded only once. For example, the drive may record an information write-inhibit signal on the disk so that erasure or rewriting cannot be performed.

[0086]

Now, the present invention will be described in further detail with reference to specific examples. However, the present invention is not limited to the following examples unless it exceeds the gist. The substrates used in Examples and Comparative Examples were all the same polycarbonate substrates obtained by injection molding, and had a refractive index of 1.56 with respect to a laser beam having a wavelength of 680 nm. Also,
Under any of the recording conditions shown in Examples and Comparative Examples, the noise level when recording on lands and the noise level when recording on grooves were almost the same. Therefore,
The comparison of the CN ratio is synonymous with the comparison of the record carrier level.

Example 1 A substrate provided with a spiral groove was prepared. The groove width and the land width were both 0.75 μm, and the groove depth was about 70 nm. On this substrate, a lower dielectric protection layer, a recording layer, an upper dielectric protection layer, and a reflection layer were provided by sputtering.

The lower dielectric protection layer and the upper dielectric protection layer are (ZnS) ₈₀ (SiO ₂ ) ₂₀ , the lower dielectric protection layer has a thickness of 100 nm, and the upper dielectric protection layer has a thickness of 20 n.
m. The recording layer is Ge, Sb, and T that cause a reversible phase change between an amorphous phase and a crystalline phase by laser irradiation.
e is used as a main component, and the composition ratio is Ge: Sb: T
e = 2: 2: 5 (atomic ratio). The thickness of the recording layer is 25
nm. The reflective layer was made of Al _97.5 Ta _2.5 at 100 nm. An ultraviolet curable resin was further provided on the reflective layer as a protective coat. Since the recording layer immediately after the film formation is in an amorphous state, the entire surface was annealed by laser light to change the phase to a crystalline state, which was an initial (unrecorded) state.

The recording is performed by irradiating a converging beam of a high power laser onto the track to change the recording layer to an amorphous state, and detecting the recording mark by the resulting change in the amount of reflected light from the amorphous recording mark. went. Next, the disk is rotated at a linear velocity of 10 m / s,
A semiconductor laser beam of 0 nm was condensed on the recording layer by an objective lens having a numerical aperture of 0.60, and signals were recorded and reproduced while performing tracking control by a push-pull method.

First, an arbitrary groove was selected, and a signal having a frequency of 7.47 MHz was recorded. Recording power of 10
One beam overwriting was performed with the erasing power and the base power changed to 6 mW while changing the power in steps of 1 mW between 12 mW. After that, it was reproduced and measured with a spectrum analyzer at a resolution bandwidth of 30 kHz. As a result, the CN ratio was a good value of 54 to 55 dB. Next, when an arbitrary land was selected and the same recording was performed to measure the CN ratio, the CN ratio was 54 to 55 dB, which was exactly the same as that for the groove.
was gotten.

The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated to be 0.01 π for the reflected light in the amorphous state. The absorption ratio A _c / A _a of the recording layer was 0.84 by calculation.

Example 2 The same disk as in Example 1 was rotated at a linear velocity of 15 m / s, an arbitrary groove was selected, and a signal having a frequency of 11 MHz was recorded using the same signal recording device as in Example 1. Recording power: 12 mW, erase power, base power: 7 mW
To perform one-beam overwriting. After that, it was reproduced and measured at a resolution bandwidth of 30 kHz.
2 dB was obtained. After recording, the recording track was irradiated with a DC laser beam having a power of 7 mW. As a result, the carrier level was reduced by 25 dB and the erasing ratio was 25 dB, indicating good erasing characteristics. Next, an arbitrary land was selected, the same recording was performed, and the CN ratio was measured. As a result, a CN ratio of 52 dB exactly equal to that of the groove was obtained, and an erasing ratio of 24 dB equivalent to that of the groove was obtained.

Example 3 A disc was produced in exactly the same manner as in Example 1 except that the composition of the recording layer was Ge ₂₂ Sb ₂₅ Te ₅₃ . The stoichiometric composition of Ge: Sb: Te = 2: 2: 5 is suitable for performing recording and reproduction at a linear velocity of 10 m / s or more, and at a linear velocity of 10 m / s or less, a recording mark by recrystallization. It is effective to slightly increase the amount of Sb in order to prevent shape distortion.

The disk was rotated at a linear velocity of 3 m / s, an arbitrary groove was selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording device as in the first embodiment. The recording power was changed between 8.5 to 10.5 mW in 0.5 mW steps, and the erasing power and the base power were set to 4.5 mW to perform one-beam overwriting. After that, reproduction and measurement were performed at a resolution bandwidth of 10 kHz. As a result, the CN ratio was a good value of 57 to 59 dB. Next, when an arbitrary land was selected and the same recording was performed to measure the CN ratio, the CN ratio was 57 to 59 dB, which was exactly the same as that for the groove.
was gotten. At this time, the jitter of the recording mark was 8 ns. The jitter was measured from the beginning to the end of the mark by detecting the zero cross point of the second derivative of the signal waveform.

The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated to be 0.01π ahead of the reflected light in the amorphous state. The absorption ratio A _c / A _a of the recording layer was 0.84 by calculation. FIG. 6 shows the relationship between the recording power and the CN ratio obtained by this embodiment.

Example 4 A disk was manufactured in the same manner as in Example 3 except that the thickness of the lower dielectric protection layer was changed to 150 nm. Rotate the disc at a linear velocity of 3 m / s, select an arbitrary groove,
Using the same signal recording device as in the first embodiment, using a frequency of 2.24M
Hz signal was recorded. The recording power was changed in steps of 0.5 mW between 10 and 12 mW, and one-beam overwriting was performed with the erasing power and the base power being 4.5 mW. After that, it was reproduced and measured at a resolution bandwidth of 10 kHz, which was a good value with a CN ratio of 54 to 55 dB.

Next, an arbitrary land was selected, the same recording was performed, and the CN ratio was measured. As a result, a CN ratio of 54 to 55 dB completely equal to that of the groove was obtained. The CN ratios of the land and the groove were equal and sufficient, but the CN ratio was reduced by about 4 dB as compared with the third embodiment, and the optimum recording power required about 1.5 mW more. Deterioration of the recording sensitivity is directly linked to a reduction in the laser light life of the drive used.

The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated, and the reflected light in the amorphous state was delayed by 0.03π. The absorption ratio A _c / A _a of the recording layer was 0.75 by calculation.

Comparative Example 1 A disk was produced in exactly the same manner as in Example 3 except that the thickness of the recording layer was changed to 20 nm. 3m / linear velocity
The sample was rotated at s, an arbitrary groove was selected, and a signal having a frequency of 2.24 MHz was recorded using the same signal recording device as in Example 1. Recording power is 1 mW between 5 and 10 mW
Erasing power and base power are changed by 4.5m
As W, one-beam overwriting was performed. After that, it was reproduced and measured with a resolution bandwidth of 10 kHz, which was a good value with a CN ratio of 56 dB.

Next, an arbitrary land was selected, the same recording was performed, and the CN ratio was measured. As a result, it was 53 dB.
As described above, the signal quality of the land and the groove was not equal, and a difference of 3 dB was caused in the CN ratio. By calculation, the phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was 0.20π ahead of the reflected light in the amorphous state. Further, the absorption ratio A _c / A _a of the recording layer is calculated to be 0.
85.

Comparative Example 2 A disk was produced in exactly the same manner as in Example 3 except that the thickness of the lower dielectric protection layer was 180 nm, the thickness of the recording layer was 20 nm, and the thickness of the upper dielectric protection layer was 80 nm. did. The disk was rotated at a linear velocity of 3 m / s, an arbitrary land was selected, and the frequency was changed to 2. using the same signal recording device as in the first embodiment.
A 24 MHz signal was recorded. Recording power is 8-9mW
, The erase power and the base power were set to 4.5 mW, and one-beam overwriting was performed. Thereafter, reproduction was performed, and the CN ratio was 50 to 51 dB when measured at a resolution bandwidth of 10 kHz.

Next, an arbitrary groove was selected, the same recording was performed, and the CN ratio was measured. As a result, only 39 to 40 dB was obtained. As described above, one of the signal qualities of the land and the groove was remarkably deteriorated, and the difference in the CN ratio was as much as 11 dB.

The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated, and the reflected light in the amorphous state was delayed by 0.16π. Absorption ratio A _{c of} recording layer
Although the calculated value of / A _a was 1.19, the jitter of the recording mark measured at the land was 13 ns.
And inferior to Example 3. FIG. 7 shows the relationship between the recording power and the CN ratio obtained by this comparative example.

Comparative Example 3 A disk was produced in exactly the same manner as in Example 3 except that the thickness of the lower dielectric protection layer was 220 nm, the thickness of the recording layer was 20 nm, and the thickness of the upper dielectric protection layer was 80 nm. did. The disk was rotated at a linear velocity of 3 m / s, an arbitrary land was selected, and the frequency was changed to 2. using the same signal recording device as in the first embodiment.
A 24 MHz signal was recorded. Recording power is 8-9mW
, The erase power and the base power were set to 4.5 mW, and one-beam overwriting was performed. After that, it was reproduced and measured with a resolution bandwidth of 10 kHz, and the CN ratio was 51 to 52 dB. next,
An arbitrary groove was selected, the same recording was performed, and the CN ratio was measured. As a result, only 44 to 45 dB was obtained.
Thus, one of the signal quality of the land and the groove was remarkably deteriorated, resulting in a difference of 7 dB in the CN ratio.

The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated to be 0.25π delayed from the reflected light in the amorphous state. Absorption ratio A _{c of} recording layer
Although the calculated value of / A _a was 1.21 as calculated, the jitter of the recording mark measured at the land was 10 ns.
And inferior to Example 3.

Example 5 A spiral groove having a groove pitch of 1.1 to 1.6 was used.
Plural pieces of which were changed to 0.5 μm at 0.5 μm intervals were prepared. In each case, the groove width and the land width were equal. The substantial recording track pitch is 0.55 to 0.8 μm. The groove depth was about 70 nm. On this substrate, a lower dielectric protection layer, a recording layer, an upper dielectric protection layer, and a reflection layer were provided by sputtering. The layer configuration was the same as in Example 1 except that the composition of the recording layer was Ge ₂₂ Sb _23.5 Te _54.5 .

The disk was repeatedly subjected to overwrite recording, and the degree of cross erase was evaluated. First, recording was performed on a groove or land, and then overwriting was repeatedly performed on both adjacent lands or grooves, and a decrease in the CN ratio of a signal recorded on the groove or land was measured first.

A disk is rotated at a linear velocity of 10 m / s,
A 680 nm semiconductor laser beam was condensed on the recording layer with an objective lens having a numerical aperture of 0.60, and signals were recorded and reproduced while performing tracking control by a push-pull method. First, an arbitrary groove was selected, and a signal having a frequency of 2.24 MHz was recorded at a duty of 25%. Recording power 8 ~
One beam overwriting was performed at 9 mW, and the erasing power and the base power were 4.5 mW.

As a result, the groove pitch was 1.45 μm
(Recording track pitch 0.725 μm) or more, the C between adjacent grooves or lands after 10,000 overwrites
The reduction of the N ratio could be made less than 3 dB, which was a level that was not problematic in practical use. The phase difference of the reflected light between the crystalline state and the amorphous state of the recording layer was calculated by calculating that the reflected light in the amorphous state advanced by 0.01π. The absorption ratio A _c / A _a of the recording layer was 0.85 by calculation.

According to the analysis results obtained by solving the heat diffusion equation of the present inventors by numerical calculation, the layer structure used in this embodiment is one of the ones having the largest heat diffusion in the lateral direction, and This means that the examination was performed under the most severe conditions. Therefore, it can be considered that there is no problem in other layer configurations as long as it is equal to or more than the minimum track pitch.

Example 6 The same disk as in Example 5 was repeatedly overwritten on a land, and the mark length jitter of a signal on the land was measured. The recording / reproducing condition is the NA of the focusing lens.
Example 5 was the same as Example 5 except that a material having a value of 0.55 was used. Only when the groove pitch 1.55μm and 1.6 [mu] m (recording track pitch 0.775μm and 0.8 [mu] m), the jitter increase over 10 ³ times overwriting was suppressed to about 20%. On the other hand, at a groove pitch of 1.4 μm (a recording track pitch of 0.7 μm),
Increase in jitter significantly, to 10 ³ times of overwriting was more than doubled.

[0112]

As described above, according to the optical recording medium and the recording / reproducing method of the present invention, an undesired difference between the carrier level of the recording mark of the land and the carrier level of the groove can be eliminated. Also when signals are recorded in both the groove and the groove, the influence of crosstalk from an adjacent track can be reduced. Therefore, the same level of reproduction signal amplitude can be obtained regardless of whether recording is performed on either the land or the groove, and a high-quality and highly reliable land and groove recording disk can be provided.

Further, the ratio of the ratio of the irradiation light absorbed by the recording layer in the case where the recording layer of the optical recording medium according to the present invention is in the amorphous state and in the case where the recording layer is in the crystalline state is specified, thereby achieving a high CN. An excellent disc having a low recording mark jitter and a low recording mark can be provided.

[Brief description of the drawings]

FIG. 1 is an enlarged perspective view for explaining a positional relationship between a groove shape of an optical disc and a convergent beam of irradiation laser light in the present invention.

FIG. 2 is an enlarged perspective view for explaining a positional relationship between a groove shape of an optical disc and a convergent beam of irradiation laser light in the present invention.

FIG. 3 is an enlarged perspective view for explaining a positional relationship between a groove shape of an optical disc and a convergent beam of irradiation laser light in the present invention.

FIG. 4 is an enlarged perspective view for explaining a positional relationship between a groove shape of an optical disc and a convergent beam of irradiation laser light in the present invention.

FIG. 5 is a schematic diagram showing the shape of a convergent beam.

FIG. 6 is a diagram showing a relationship between a recording power and a CN ratio in Example 3.

FIG. 7 is a diagram showing the relationship between recording power and CN ratio in Comparative Example 2.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 recording layer 3 land 4 groove 5 convergent beam 6 area of convergent beam irradiated to land 7 area of convergent beam irradiated to groove 8 recording mark 9 convergent beam 10 intensity distribution of convergent beam 11 Airy disk 12 focusing lens

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Takada 3--10, Utsudori, Kurashiki-shi, Okayama Prefecture Mitsubishi Chemical Mizushima Office

Claims (5)

[Claims] 1. A structure in which a lower dielectric protection layer, a phase-change recording layer, an upper dielectric protection layer, and a metal reflection layer are sequentially laminated on a transparent substrate having a groove formed therein. An optical recording medium for recording, erasing, and reproducing information by irradiating a laser beam having a wavelength of 700 nm or less using both of them as recording areas, and (1) reflected light from an unrecorded area defined below. And the phase difference of the reflected light from the recording area α α = (the phase of the reflected light from the unrecorded area) − (the phase of the reflected light from the recorded area) satisfies the following equation. 1) π ≦ α ≦ (m + 0.1) π (m is an integer) (2) The groove width GW, the width LW between grooves, and the groove depth d satisfy the following formula: 0.3 μm ≦ GW ≦ 0.8 μm (Equation 3) 0.3 μm ≦ LW ≦ 0.8 μm (Equation 4) 0.62 × (λ / NA) ≦ LW 0.
8 × (λ / NA) (5) (GW + LW) / 2> 0.6 × (λ / N
A) ## EQU6 ## λ / 7n <d <λ / 5n (where, λ: wavelength of irradiation light, n: refractive index of substrate, N
A: Numerical aperture of the focusing lens). 2. The absorptance of an irradiation laser beam in a recording layer,
When the recording layer is in a crystalline state, A _c , and when the recording layer is in an amorphous state, A _a , the ratio A _c / A _a of the absorptivity between the crystalline state and the amorphous state is 0.84. ≦ _{a c} / a _a <optical recording medium according to claim 1, characterized in that 1.01. 3. The reflection layer is an alloy of Al and Ti or Ta, and the content of Ti or Ta is 0.5 to 3.5 at%.
The optical recording medium according to claim 1, wherein 4. One or both of the lower dielectric protection layer and the upper dielectric protection layer are a mixed film of ZnS and one of SiO _{2 and} Y ₂ O ₃ ,
The optical recording medium according to claim 1 content of ₂ or Y ₂ O ₃ is characterized in that it is a 5 to 40 mol%. 5. The optical recording medium according to claim 1, wherein both grooves are used as recording regions, and recording, erasing, and erasing are performed in each region by one-beam overwriting of a laser having a wavelength of 700 nm or less. A recording / reproducing method characterized by reproducing.