JP3029690B2 - Information recording medium and information recording method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium, and more particularly to a phase change type information recording medium which irradiates a light beam to cause a phase change in a recording layer material to record and reproduce information. In addition, the present invention relates to a rewritable information recording medium, and is applied to an optical memory-related device, particularly to a rewritable compact disc (CD).

[0002]

2. Description of the Related Art As one of optical memory media capable of recording, reproducing and erasing information by irradiating an electromagnetic wave, particularly a laser beam, a so-called phase change utilizing a transition between a crystal and an amorphous phase or between a crystal and a crystal phase. Type optical information recording media are well known. In particular, overwriting with a single beam, which is difficult with a magneto-optical memory, is possible, and the drive side optical system is simpler. Typical recording materials include Ge-Te, Ge-Te-Sb-S, and Ge-Te- as disclosed in US Pat. No. 3,530,441.
S, Ge-Se-S, Ge-Se-Sb, Ge-As-
So-called chalcogen-based alloy materials such as Se, In-Te, Se-Te, and Se-As can be used. Also, stability,
Au is added to Ge-Te system for the purpose of improving high-speed crystallization, etc.
(Japanese Unexamined Patent Publication (Kokai) No. 61-219902), Sn and Au (Japanese Unexamined Patent Publication (Kokai) No. 61-270190), Pd (Japanese Unexamined Patent Publication (Kokai) No. 62-1949).
0), etc., and a material having a specified Ge-Te-Se-Sb composition ratio (JP-A-62-73438) for the purpose of improving the repetition performance of recording / erasing. I have. However, none of them can satisfy all of the properties required for a phase-change rewritable optical memory medium.

Japanese Patent Application Laid-Open No. 63-251290 discloses an optical information recording medium (hereinafter abbreviated as "optical recording medium") having a recording layer formed of a single phase of a multi-component compound having a ternary or higher crystalline state. May be proposed). As used herein, “substantially ternary or more ternary compound single phase” refers to a compound having a ternary or more stoichiometric composition (eg, In ₃ SbT
The e _2, etc.) in the recording layer is intended to include 90 atomic% or more. The use of such a recording layer enables high-speed recording and high-speed erasing. However, in this case, the laser power required for recording and erasing is not yet sufficient, and the erasing ratio is low (the erasure remains large).
And the like. Further, JP-A-1-277338
The JP _{(Sb a Te 1-a)} 1-Y M Y ( here 0.4
≦ a <0.7, Y ≦ 0.2, and M is Ag, Al, A
s, Au, Bi, Cu, Ga, Ge, In, Pb, P
At least one selected from the group consisting of t, Se, Si, Sn and Zn. An optical recording medium having a recording layer made of an alloy having a composition represented by (1) has been proposed. The basis of this system is Sb ₂ Te ₃ , and when Sb is excessive, high-speed erasing and repetition characteristics are improved, and addition of M promotes high-speed erasing. In addition, the erasing rate by DC light is also high. However, in this document,
The erasing rate at the time of writing is not shown (results of studies by the present inventors have revealed unerased portions), and the recording sensitivity is insufficient.

Similarly, in Japanese Patent Application Laid-Open No. Sho 60-177446, (In _{1 -X} Sb _X ) _{1 -Y} M _Y (0.55 ≦
X ≦ 0.80, 0 ≦ Y ≦ 0.20, M is Au, A
g, Cu, Pd, Pt, Al, Si, Ge, Ga, S
n, Te, Se, and Bi. ), And JP-A-63-228433 discloses that the recording layer is made of Ge.
Although an alloy of Te—Sb ₂ Te ₃ —Sb (excess) is used, none of them satisfy characteristics such as sensitivity and erasing ratio. As has been seen so far, in the optical recording medium, particularly, the recording sensitivity and the erasing sensitivity are improved, the erasing ratio is prevented from being reduced due to the unerased portion during overwriting, and the life of the recorded and unrecorded portions is prolonged. This is the most important issue to be solved. As one of means for solving these problems, there has been proposed a technique of providing a chemically stable protective layer having good heat resistance above and below a recording layer (Japanese Patent Application Laid-Open No. 61-5450, 6).
3-259855). The functions required of the heat-resistant protective layer include transparency to laser light, a high melting point with respect to operating temperature, high mechanical strength, and high chemical stability. In the case of a recording layer, particularly a recording layer using a chalcogen-based compound, a chemically inactive protective material has a very important meaning since the chalcogen element is active.

In this respect, oxide-based dielectric materials generally used cannot be said to sufficiently meet the demand. Further, the heat-resistant protective layer also has a function as a heat dissipation layer (heat transfer layer). In general, when the heat dissipation layer has too low thermal conductivity, the quenching effect required for amorphization cannot be obtained, and when it is too large, heat cannot be effectively used, that is, the slow cooling condition required for crystallization is insufficient. However, the recording / erasing sensitivity was lowered. As described above, it is necessary to control the heat radiation layer to have a thermal conductivity suitable for the recording film. However, it was difficult to control the thermal conductivity over a wide range with the above-mentioned materials. For example, when the linear velocity is 3 m / s or less, particularly at a low linear velocity of about 1.2 to 1.4 m / s, which is the standard for compact discs, the cooling rate of heat generated during recording (at the time of laser light absorption) This is likely to be insufficient, so that good recording marks cannot be obtained.

[0006]

(1) The present invention solves all of the above problems in the prior art, has high recording sensitivity and erasing ratio, and has a C / N ratio due to repetition of recording / erasing.
A rewritable information recording medium that can be recorded without deterioration and has a long life and does not require a complicated system, and
(2) To provide a rewritable compact disc.

Means for Solving the Problems The structure of the present invention for solving the above problems is an information recording medium and an information recording method using the same as described in the claims. When this structure is specifically described, the lower heat-resistant protective layer is not always necessary, but when the substrate is made of a material having low heat resistance such as, for example, a polycarbonate resin, it is desirable to provide the lower heat-resistant protective layer.

Due to the combination of the recording layer and the upper heat-resistant protective layer laminated thereon, even at a low linear velocity of 1.2 to 1.4 m / sec, rapid cooling conditions during recording (amorphization) and erasure (crystal ) Can be simultaneously satisfied, and good recording / reproducing characteristics can be obtained. The recording layer of the present invention can be formed by various vapor phase epitaxy methods, for example, a vacuum evaporation method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam evaporation method and the like. In addition to the vapor phase growth method, a wet process such as a sol-gel method can be applied. The thickness of the recording layer is 200 to 10
000 °, preferably 400-3000 °. When the thickness is less than 200 °, the light absorbing ability is remarkably reduced, and does not serve as a recording layer. On the other hand, if the thickness is more than 10,000 °, uniform phase change at high speed is unlikely to occur.

[0008] The material of the substrate is usually glass, ceramics,
Alternatively, it is a resin, and a resin substrate is suitable in terms of moldability, cost, and the like. Representative examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin and the like. Polycarbonate resin in terms of workability, optical properties, etc.,
Acrylic resins are preferred. Materials for the lower heat-resistant protective layer include SiO, SiO ₂ , ZnO, SnO ₂ , and Al.
Metal oxides such as ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , nitrides such as Si ₃ N ₄ , AlN, TiN, BN, ZrN, ZnS, In ₂ S ₃ , TaS _{4 and the} like Sulfide, Si
Examples thereof include carbides such as C, TaC, B ₄ C, WC, TiC, and ZrC, diamond-like carbon, and mixtures thereof. These materials can be used alone as a protective layer, or as a mixture of each other. Further, it may contain impurities as needed. However, the melting point of the heat-resistant protective layer needs to be higher than the melting point of the recording layer. Such a heat-resistant protective layer can be formed by various vapor deposition methods, for example, a vacuum deposition method, a sputtering method, a plasma CVD method, and a photo CVD method.
It can be formed by a method, an ion plating method, an electron beam evaporation method, or the like.

The heat-resistant protective layer has a thickness of 200 to 50.
00 °, preferably 500-3000 °.
When the thickness is less than 200 °, the function as the heat-resistant protective layer is not fulfilled. On the other hand, when the thickness is more than 5000 °, the sensitivity is lowered or the interface is liable to peel off. or,
If necessary, the protective layer can be multi-layered. As the reflective layer, a metal material such as Al or Au, or an alloy thereof can be used. Such a reflective layer can be formed by various vapor deposition methods, for example, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam deposition method, or the like. Here, the hard carbon film used for the upper heat-resistant protective layer is a hard carbon film (i-C film, diamond-like carbon film containing at least one of amorphous and microcrystalline materials using carbon atoms and hydrogen atoms as main structure-forming elements). , An amorphous diamond film and a diamond thin film). One of the features of the hard carbon film is that it is a vapor-grown film, so that its physical properties can be controlled over a wide range by film-forming conditions, as described later.

In order to further widen the range of controlling physical properties, the hard carbon film contains at least 5 group% element of the periodic table as one of the constituent elements with respect to all constituent atoms.
Hereinafter, the group IV element is also not more than 35 atomic%, and
Group element 5% or less, alkaline earth metal element 5% or less, alkali metal element 5% or less, nitrogen atom 5% or less, oxygen atom 5% or less, chalcogen element 35% or less Below, or 35 atomic% of halogen elements
It may be contained in the following amount. The amounts of these elements or atoms can be measured by a conventional method of elemental analysis, for example, Auger analysis. In addition, the amount can be adjusted by the amount of other compounds contained in the source gas and the film forming conditions. To form such a hard carbon film, an organic compound gas, particularly a hydrocarbon gas, is used. The phase state of these raw materials does not necessarily need to be a gas phase at normal temperature and normal pressure, but any liquid phase or solid phase can be used as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression. . Examples of the hydrocarbon gas as a raw material gas include paraffinic hydrocarbons such as CH ₄ , C ₂ H ₈ and C ₄ H ₂₀ ,
Gases containing at least all hydrocarbons such as olefin-based hydrocarbons such as ₂ H ₄ , diolefin-based hydrocarbons, acetylene-based hydrocarbons, and aromatic hydrocarbons can be used.

In addition, other than hydrocarbons, compounds such as alcohols, ketones, ethers, and esters containing at least a carbon element can be used. As a method for forming a hard carbon film from a raw material gas in the present invention, a method in which a film forming active species is formed through a plasma state generated by a plasma method using direct current, low frequency, high frequency or microwave is preferable. However, a method using a magnetic field effect is more preferable for performing deposition under a low pressure for the purpose of increasing the area, improving the uniformity, and / or forming a film at a low temperature. Active species can also be formed by thermal decomposition at high temperatures.

An example of the conditions for depositing the hard carbon film thus produced is generally as follows in the case of the CVD method. RF output: 0.1 to 50 W / cm ² Pressure: 10 ^{−3 to} 10 Torr Deposition temperature: room temperature to 950 ° C., preferably room temperature to 300 ° C. The raw material gas is decomposed into radicals and ions by this plasma state and reacts with each other.
And a hydrogen atom H, a hard carbon film containing at least one of amorphous (amorphous) and microcrystalline (crystal size is several tens to several μm) is deposited. Table 1 shows properties of the hard carbon film.

[0013]

[Table 1]

Note) Measuring method; Specific resistance (ρ): Determined from the IV characteristics of a coplanar cell. Optical band gap (Egopt): calculated absorption coefficient (alpha) from the spectral ^{characteristics, (αhν) 1/2 =} B (hν'-E
gopt). Hydrogen content in film (C _H ): 2900 from infrared absorption spectrum
The peak near cm ^-1 is integrated and multiplied by the absorption cross section A to obtain the peak. That is, C _H = A∫Δα (w) / w ・ dw SP ³ / SP ² ratio: Infrared absorption spectrum is calculated as SP ³ , SP ²
Is decomposed into Gaussian functions respectively belonging to the above, and is obtained from the area ratio. Vickers hardness (H): According to a micro Vickers meter. Refractive index (n): by ellipsometer.

The hard carbon film thus formed was analyzed by IR absorption method and Raman spectroscopy.
^It has been revealed that interatomic bonds forming hybrid orbitals ³ and SP ² are mixed. The ratio of SP ³ bonds to SP ² bonds can be roughly estimated by separating peaks in the IR spectrum. The IR spectrum shows 280
The spectrum of many modes overlaps and is measured from ⁰ to 3150 cm ^-1 , but the assignment of the peak corresponding to each wave number is clear, the peak is separated by Gaussian distribution, and the peak area is calculated. By calculating the ratio, SP ³ / SP ² can be known. According to the X-ray and electron diffraction distribution, the hard carbon film is in an amorphous state (a-C: H) and / or several tens of degrees.
It can be seen that it is in an amorphous state containing fine crystal grains of about several μm.

In general, in the case of the plasma CVD method suitable for mass production, the smaller the RF output, the higher the specific resistance and hardness of the film, and the lower the pressure, the longer the life of the active species. There is a tendency that the temperature is lowered and the large area is made uniform, and the specific resistance and hardness are increased. Further, since the plasma density decreases at low pressure, the method using the magnetic field confinement effect is particularly effective for increasing the specific resistance. Furthermore, this method (plasma CVD method) is performed at room temperature to
Since it has a feature that a high-quality hard carbon film can be similarly formed even at a relatively low temperature condition of about 150 ° C., it is most suitable for lowering the temperature of an information recording medium manufacturing process. Therefore, there is a feature that the degree of freedom in selecting a substrate material to be used is widened and a uniform film can be obtained over a large area because the substrate temperature is easily controlled. As shown in Table 1, the structure and physical properties of the hard carbon film can be controlled in a wide range, so that there is an advantage that the characteristics can be freely designed. Furthermore, since the hardness of the film is high, the damage is small, and the yield is improved from this point as well. The thickness of the hard carbon film is more preferably 200 to 6000 °. The number of defects in the element due to pinholes in the hard carbon film increases as the film thickness decreases, and becomes particularly remarkable at 300 ° or less (the defect rate exceeds 1%).
In addition, uniformity of the in-plane distribution of the film thickness (and hence, uniformity of the element characteristics) cannot be ensured (the accuracy of the film thickness control is limited to about 30 ° and the variation of the film thickness exceeds 10%). More preferably, the thickness is 300 ° or more.

Further, in order to make it difficult for the hard carbon film to peel off due to stress, the film thickness is more desirably 4000 ° or less. In consideration of these factors, the thickness of the hard carbon film is more preferably 300 to 4000 °. When graphite is used in place of the hard carbon film as the material of the upper heat-resistant protective layer, the physical properties of the graphite are as follows: melting point: 3000 ° C. or higher; density: 2.0 to 2.5 g / cm.
^{3. A} material having a thermal conductivity of 0.1 to 0.5 cal / cm · S · ° C. is suitable. Further, the composition does not need to be pure graphite, and may partially include a diamond structure, defects, impurities and the like. The method for forming the upper heat-resistant protective layer can be the same as the method for forming the lower heat-resistant protective layer, but the sputtering method is a preferred method.

[0018]

The present invention will be specifically described below with reference to examples. Example I-1 A groove having a pitch of 1.6 μm and a depth of 700 °, a thickness of 1.2
The lower heat-resistant protective layer, the recording layer, the upper heat-resistant protective layer, and the reflective layer were sequentially laminated on a polycarbonate substrate having a diameter of 1200 mm and a diameter of 1200 mm according to the configuration shown in Table 2.

[0019]

[Table 2]

The evaluation of the optical disk was carried out by using a 830 nm semiconductor laser beam by N.I. A. Irradiation was performed from the substrate side through an objective lens of = 0.5, and narrowed down to a spot diameter of about 1 μmφ on the medium surface. The recording film immediately after film formation is amorphous. At the time of measurement, first, the entire surface of the disk was sufficiently crystallized with 5 mW DC light on the medium surface, and was brought into an initial (unrecorded) state. At this time, the rotational linear velocity of the disk is 1.
It was constant at 3 m / s. Next, the writing power is 3 to 10 mW.
The recording performance was evaluated at a pulse width of 690 ns while changing the recording performance by 1 mW at a time. The reproduction light was constant at 1.0 mW. As a result, a signal having a C / N of 45 dB or more was obtained at 5 to 10 mW. Further, when the recording mark was erased with a DC light of 5 mW, the recording mark was almost completely erased, and the unerased portion was not recognized. Example I-2 A disk was prepared and evaluated in the same manner as in Example I-1, except that the composition of the recording layer material was changed to Ag ₁₀ In ₁₀ Te ₂₀ Sb ₆₀ .

Comparative Example I-1 The same evaluation was performed as in Example I-1, except that the composition of the recording layer material was changed to Ag ₅ In ₅ Te ₁₀ Sb ₈₀ . Comparative Example I-2 The upper protective layer was the same as the lower protective layer [ZnS + SiO ₂ (2
0%)] A disk having the same layer configuration as that of Example I-1 except that the composite dielectric layer was used, and the same evaluation was performed. Except that the Comparative Example I-3 recording layer was Ag ₂₅ In ₂₅ Te ₃₅ Sb ₁₅ was subjected to the same evaluation as in Example I-1. Table 3 summarizes the results.

[0022]

[Table 3]

Example II-1 An optical disk was manufactured under the same conditions as in Example I-1 except that the material of the upper heat-resistant protective layer was changed to graphite, and a test was conducted under the same conditions. 5-10W
As a result, a signal of C / N of 45 dB or more was obtained. In addition, 5mW
As a result, the recorded mark was almost completely erased, and the unerased portion was not recognized. To prepare a disk, except that the composition of Example II-2 recording layer material was replaced with Ag ₁₀ In ₂₀ Te ₂₀ Sb ₅₀ in the same manner as in Example II-1, was evaluated in the same manner.

Comparative Example II-1 The same evaluation as in Example II-1 was carried out except that the composition of the recording layer material was changed to Ag ₅ In ₅ Te ₁₀ Sb ₈₀ . Comparative Example II-2 Same as Example II-1 except that the recording layer was Ag ₁₀ In ₁₀ Te ₂₀ Sb ₆₀ and the upper protective layer was the same [ZnS + SiO ₂ (20%)] composite dielectric layer as the lower protective layer. A disk having the above layer configuration was produced, and the same evaluation was performed. Comparative Example II-3 Example except that the recording layer was made of Ag ₁₅ In ₃₀ Te ₃₀ Sb ₂₅
The same evaluation as II-1 was performed. Table 4 summarizes the results.

[0025]

[Table 4]

[0026]

The effects of the present invention described above are summarized as follows. (1) By combining a recording layer material having a good crystal-amorphous transition characteristic and an upper heat-resistant protective layer having a good thermal conductivity, excellent recording can be performed even under a low linear velocity of 1.2 to 1.4 m / sec. A phase change type information recording medium having erasing performance was obtained. (2) A rewritable compact disc can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the configuration of an information recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower heat-resistant protective layer 3 Recording layer 4 Upper heat-resistant protective layer 5 Optical reflection layer

Continuation of front page (72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-2-151481 (JP, A) JP-A-2-249686 (JP, a) JP flat 2-64937 (JP, a) JP flat 2-112986 (JP, a) JP Akira 57-205193 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) B41M 5/26 G11B 7/24 506

Claims (4)

(57) [Claims] 1. A rewritable information recording medium for recording, erasing, and reproducing information by irradiating a laser beam,
On a substrate, a recording layer, an upper heat-resistant protective layer, which are sequentially laminated optical reflective layer, the heat-resistant protective layer, a plasma C
An information recording medium, which is a hard carbon film formed by a VD method , and wherein the recording layer contains a phase-change recording material represented by the following general formula as a main component. General formula Ag _α In _β Te _γ Sb _δ where 5 ≦ α ≦ 226 6 ≦ β ≦ 24 13 ≦ γ ≦ 44 18 ≦ δ ≦ 77 α + β + γ + δ = 100 2. The information recording medium according to claim 1, wherein the upper heat-resistant protective layer is a film containing graphite as a main component. 3. The information recording medium according to claim 1, further comprising a lower heat-resistant protective layer between the substrate and the recording layer. 4. The recording layer is irradiated with laser light from the substrate side while rotating the information recording medium according to claim 1 at a constant linear speed of 1.2 to 1.4 m / sec. An information recording method comprising recording a signal.