JPH05185731A - Information recording medium and method for recording information using the same - Google Patents

Abstract

PURPOSE:To provide an information-recording medium which has a high recording sensitivity and an elimination ratio and allows rewriting without C/N deterioration end to provide a method for recording information using the medium. CONSTITUTION:In a information recording medium, a recording layer 3, heat- resistant protecting layers 2, 4, and a photo-reflecting layer 5 are formed on a substrate 2. The heat-resistant protecting layer 4, in particular, is a hard carbon film or a graphite layer, and the recording layer is composed of a material represented by AgalphaInbetaTegammaSbdelta, where 5<=alpha<=22, 6<=beta<=24, 13<=gamma<=44, 18<=delta<=77 and alpha+beta+gamma+delta=100.

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, particularly a phase change type information recording medium, which causes a phase change in a recording layer material by irradiating a light beam to record and reproduce information. In addition, the present invention relates to a rewritable information recording medium, and is applied to optical memory-related equipment, particularly 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 irradiation of electromagnetic waves, especially laser beams, so-called phase change utilizing a transition between a crystal-amorphous phase or a crystal-crystal phase. A type optical information recording medium is well known. In particular, magneto-optical memory allows overwriting with a single beam, which is difficult, and the optical system on the drive side is simpler. Typical recording materials thereof are Ge-Te, Ge-Te-Sb-S and Ge-Te- as disclosed in USP 3,530,441.
S, Ge-Se-S, Ge-Se-Sb, Ge-As-
Examples include so-called chalcogen-based alloy materials such as Se, In-Te, Se-Te, and Se-As. Also stability,
Au was added to the Ge-Te system for the purpose of improving high-speed crystallization.
(JP-A-61-2196992), Sn and Au (JP-A-61-270190), Pd (JP-A-62-1949).
0) or the like, or a material (Ge-Te-Se-Sb) having a specified composition ratio (Japanese Patent Laid-Open No. 62-73438) for the purpose of improving the repetitive recording / erasing performance. There is. However, none of them can satisfy all of the characteristics required for a phase change type rewritable optical memory medium.

Further, Japanese Patent Laid-Open No. 63-251290 discloses an optical information recording medium having a recording layer formed of a multi-component compound single phase whose crystal state is substantially ternary or more (hereinafter abbreviated as "optical recording medium"). May be done) is proposed. Here, “substantially ternary or higher multi-component compound single phase” means a compound having a stoichiometric composition of ternary or higher (for example, In ₃ SbT).
e ₂ ) is contained in the recording layer in an amount of 90 atomic% or more. The use of such a recording layer enables high-speed recording and high-speed erasing. However, with this type, the laser power required for recording and erasing is not yet sufficient, and the erasing ratio is low (the unerased portion is large).
It has drawbacks such as Furthermore, 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
It is 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 (4) has been proposed. The basis of this system is Sb ₂ Te ₃ , and excess Sb improves high-speed erasing and repetitive characteristics, 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 erasure were found in the examination results of the present inventors), and the recording sensitivity is insufficient.

Similarly, in JP-A-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, Bi. ) Alloy, and Ge in the recording layer in JP-A-63-228433.
Although using a Te-Sb ₂ Te ₃ -Sb (excessive) comprising alloy, both the sensitivity, it does not satisfy the characteristics such as erase ratio. As seen so far, in the optical recording medium, in particular, the recording sensitivity and the erasing sensitivity are improved, the reduction of the erasing ratio due to the unerased portion at the time of overwriting is prevented, and the life of the recorded portion and the unrecorded portion is extended. It is the most important issue to be solved. As one of means for solving these problems, there has been proposed a technique in which protective layers which are chemically stable and have good heat resistance are provided above and below the recording layer (JP-A-61-2450, 6).
3-259855). Functions required of the heat-resistant protective layer include transparency to laser light, high melting point at operating temperature, high mechanical strength, and high chemical stability. In the case of a recording layer, particularly a recording layer using a chalcogen compound, a chalcogen element is active, and therefore, a chemically inactive protective material is extremely important.

In this respect, the oxide-based dielectric materials and the like 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). Generally, if the thermal conductivity of the heat dissipation layer is too small, the quenching effect required for amorphization cannot be obtained, and if it is too large, the heat cannot be effectively utilized, that is, the slow cooling conditions required for crystallization are However, the recording and erasing sensitivity was lowered. Thus, the heat dissipation layer needs to be controlled to have a thermal conductivity adapted to the recording film. However, it has been difficult to control the thermal conductivity over a wide range with the above material group. For example, when the linear velocity is 3 m / s or less, particularly when the linear velocity is a low linear velocity of about 1.2 to 1.4 m / s, which is a standard for compact discs, the cooling rate of heat generated during recording (when absorbing laser light) is Insufficiency is likely to occur, and good recording marks cannot be obtained.

[0006]

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

The constitution of the present invention for solving the above-mentioned problems is an information recording medium as described in the claims and an information recording method using the same. To explain this structure in detail, 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 polycarbonate resin, it is desirable to provide the lower heat-resistant protective layer.

By combining the recording layer with the upper heat-resistant protective layer laminated thereon, the quenching condition and erasing (crystal) during recording (amorphization) are achieved even at a low linear velocity of 1.2 to 1.4 m / sec. It is possible to satisfy the slow cooling conditions at the same time, and obtain good recording / reproducing characteristics. The recording layer of the present invention can be formed by various vapor phase growth methods such as vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, ion plating method and electron beam evaporation method. Besides the vapor phase growth method, a wet process such as a sol-gel method can also be applied. The thickness of the recording layer is 200 to 10
000Å, preferably 400 to 3000Å. When the thickness is less than 200Å, the light absorption ability is remarkably lowered and the recording layer cannot serve as a recording layer. If it is thicker than 10000Å, uniform phase change at high speed is difficult to occur.

The substrate material is usually glass, ceramics,
Alternatively, it is a resin, and a resin substrate is preferable in terms of moldability, cost, and the like. Typical examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicon resin, fluorine resin, ABS resin, urethane resin and the like. , In terms of workability and optical properties, polycarbonate resin,
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 and ZrO ₂ , nitrides such as Si ₃ N ₄ , AlN, TiN, BN and ZrN, ZnS, In ₂ S ₃ and TaS ₄ etc. 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 may be used alone as the protective layer, but may also be a mixture with each other. Further, it may contain impurities as necessary. However, the melting point of the heat-resistant protective layer needs to be higher than that of the recording layer. Such a heat-resistant protective layer may be formed by various vapor deposition methods such as vacuum deposition method, sputtering method, plasma CVD method, and photo CVD method.
Method, ion plating method, electron beam evaporation method, or the like.

The thickness of the heat resistant protective layer is 200 to 5000
Å, preferably 500 to 3000 Å. If it is thinner than 200Å, it will not function as a heat resistant protective layer,
On the other hand, when the thickness is more than 5000Å, the sensitivity is lowered and the interfacial peeling is likely to occur. Further, the protective layer may be multi-layered if necessary. Al, A as the reflective layer
A metal material such as u or an alloy thereof can be used. Such a reflective layer may be formed by various vapor deposition methods such as vacuum deposition method, sputtering method, plasma CVD method,
It can be formed by a photo CVD method, an ion plating method, an electron beam evaporation 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, at least one of amorphous and microcrystalline) having carbon atoms and hydrogen atoms as main texture-forming elements. Amorphous diamond film, also called diamond thin film)
It consists of One of the characteristics of the hard carbon film is the vapor phase growth film, so that its various physical properties can be controlled in a wide range by the film forming conditions, as will be described later.

In this hard carbon film, in order to further expand the physical property control range, at least 5 Group% of the periodic table group III element is contained as one of the constituent elements with respect to all the constituent atoms.
The same applies to group IV elements of 35 atom% or less, and group V
Group elements 5 atomic% or less, alkaline earth metal elements 5 atomic% or less, alkali metal elements 5 atomic%, nitrogen atoms 5 atomic% or less, oxygen atoms 5 atomic% or less, chalcogen-based elements 35 atomic% Or less, or 35 atom% halogen element
You may contain in the following amounts. The amounts of these elements or atoms can be measured by a conventional method of elemental analysis, such as Auger analysis. Further, the amount of this can be adjusted depending on the amounts of other compounds contained in the source gas and the film forming conditions. In order to form such a hard carbon film, an organic compound gas, especially a hydrocarbon gas is used. The phase state of these raw materials does not necessarily have to be a gas phase at room temperature and atmospheric pressure, and a liquid phase or a solid phase can be used as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or pressure reduction. .. Examples of the hydrocarbon gas as the raw material gas include paraffin hydrocarbons such as CH ₄ , C ₂ H ₈ and C ₄ H ₂₀ , and C.
Gases containing at least all hydrocarbons such as olefinic hydrocarbons such as ₂ H ₄ , diolefinic hydrocarbons, acetylene hydrocarbons, and aromatic hydrocarbons can be used.

In addition to hydrocarbons, for example, compounds such as alcohols, ketones, ethers, esters and the like 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 utilizing a magnetic field effect is more preferable for causing the deposition under a low pressure for the purpose of increasing the area, improving the uniformity and / or forming the film at a low temperature. In addition, active species can also be formed by thermal decomposition at high temperature. In addition, it may be formed through an ionic state generated by an ionization vapor deposition method, an ion beam vapor deposition method, or the like, or may be formed from neutral particles generated by a vacuum vapor deposition method, a sputtering method, or the like, Further, it may be formed by a combination thereof.

In the case of the CVD method, an example of the deposition conditions of the hard carbon film thus produced is as follows. 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. In this plasma state, the source gas is decomposed into radicals and ions and reacts with each other, whereby carbon atoms C
A hard carbon film containing at least one of amorphous (amorphous) and microcrystalline (the size of the crystal is several tens of .mu.m to several .mu.m) composed of and hydrogen atoms H is deposited. Table 1 shows various characteristics of the hard carbon film.

[0013]

[Table 1]

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

The hard carbon film thus formed was analyzed by IR absorption and Raman spectroscopy, and as a result, carbon atoms became SP.
^It has been clarified that the interatomic bonds forming the hybrid orbital ^{3 and} the hybrid orbital SP ² are mixed. The ratio of SP ³ bond to SP ² bond can be roughly estimated by separating peaks in the IR spectrum. 280 in the IR spectrum
The spectra of many modes are measured at ⁰ to 3150 cm ⁻¹ , but the attribution of the peaks corresponding to each wave number is clear, and the peak areas are calculated by separating the peaks by the Gaussian distribution. , SP ³ / SP ² can be known by obtaining the ratio. In addition, the above-mentioned hard carbon film is in an amorphous state (aC: H), and / or several tens of Å ~ according to X-ray and electron diffraction distribution.
It can be seen that it is in an amorphous state containing fine crystal grains of about several μm.

In the case of the plasma CVD method, which is generally suitable for mass production, the smaller the RF output, the more the specific resistance value and hardness of the film increase, and the lower the pressure, the longer the life of 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. Since the plasma density decreases at lower pressure, the method of utilizing the magnetic field confinement effect is particularly effective for increasing the specific resistance. Furthermore, this method (plasma CVD method)
Since it has a feature that a good quality hard carbon film can be formed even under a relatively low temperature condition of about 150 ° C., it is optimal for lowering the temperature of the information recording medium manufacturing process. Therefore, the flexibility of selection of the substrate material to be used is widened, and the substrate temperature can be easily controlled, so that a uniform film can be obtained in a large area. Since the structure and physical properties of the hard carbon film can be controlled in a wide range as shown in Table 1, there is also an advantage that the characteristics can be freely designed. Further, since the hardness of the film is high, the damage is small, and the yield is improved also from this point. The thickness of the hard carbon film is more preferably 200 to 6000Å. The number of defects in the element due to pinholes in the hard carbon film increases as the film thickness decreases, and becomes particularly noticeable below 300 Å (the defect rate exceeds 1%).
In addition, the uniformity of the in-plane distribution of the film thickness (and eventually the uniformity of the device characteristics) cannot be ensured (the film thickness control accuracy is limited to about 30Å, and the film thickness variation exceeds 10%). It is more desirable that the thickness is 300Å or more.

Further, in order to prevent the hard carbon film from peeling off due to stress, it is more preferable that the film thickness is 4000 Å or less. Taking these factors into consideration, it is more preferable that the thickness of the hard carbon film is 300 to 4000 Å. When graphite is used instead of the hard carbon film as the material of the upper heat-resistant protective layer, the physical properties of the graphite are a melting point of 3000 ° C. or higher and a density of 2.0 to 2.5 g / cm 3.
³ , those having a thermal conductivity of 0.1 to 0.5 cal / cm · S · ° C are suitable. 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 may be the same as the method for forming the lower heat-resistant protective layer, but the sputtering method is the preferred method.

[0018]

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

[0019]

[Table 2]

The evaluation of the optical disk was carried out by using a semiconductor laser beam of 830 nm as N. A. The irradiation was performed from the substrate side through the objective lens of 0.5, and the spot diameter was narrowed down to 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 by DC light of 5 mW on the medium surface to make it into an initial (unrecorded) state. The rotational linear velocity of the disk at this time is 1.
It was kept constant at 3 m / s. Next, write power 3 to 10 mW
The recording performance was evaluated with a pulse width of 690 ns while varying by 1 mW each. The reproduction light was constant at 1.0 mW. As a result, a signal of C / N of 45 dB or more was obtained at 5 to 10 mW. Further, when the recording mark was erased with 5 mW of DC light, the recording mark was almost completely erased and no unerased residue was observed. To prepare a disk, except that the composition of Example I-2 recording layer material was replaced with Ag ₁₀ In ₁₀ Te ₂₀ Sb ₆₀ in the same manner as in Example I-1, was evaluated in the same manner.

Comparative Example I-1 The same layer constitution as in Example I-1 was used except that the composition of the recording layer material was Ag ₅ In ₅ Te ₁₀ Sb _80, and the same evaluation was carried out. 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 structure as in Example I-1 was prepared except that the composite dielectric layer was used, and the same evaluation was performed. Comparative Example I-3 The same evaluations as in Example I-1 were performed except that the recording layer was Ag ₂₅ In ₂₅ Te ₃₅ Sb ₁₅ . The results are summarized in Table 3.

[0022]

[Table 3]

Example II-1 An optical disk was prepared under the same conditions as in Example I-1 except that graphite was used as the material for the upper heat-resistant protective layer, and the test was conducted under the same conditions. 5-10W
A signal of C / N 45 dB or more was obtained at. Furthermore, 5mW
When it was erased with DC light, the recording marks were almost completely erased, and no unerased residue was observed. Example II-2 A disc was prepared and evaluated in the same manner as in Example II-1 except that the composition of the recording layer material was changed to Ag ₁₀ In ₂₀ Te ₂₀ Sb ₅₀ .

Comparative Example II-1 The same layer constitution as in Example II-1 was used except that the composition of the recording layer material was Ag ₅ In ₅ Te ₁₀ Sb _80, and the same evaluation was carried out. 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 layer structure of was prepared and the same evaluation was performed. Comparative Example II-3 Example except that the recording layer was changed to Ag ₁₅ In ₃₀ Te ₃₀ Sb ₂₅
The same evaluation as II-1 was performed. The results are summarized in Table 4.

[0025]

[Table 4]

[0026]

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

[Brief description of drawings]

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

[Explanation of symbols]

 1 substrate 2 lower heat-resistant protective layer 3 recording layer 4 upper heat-resistant protective layer 5 optical reflection layer

Front page continuation (72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A rewritable information recording medium for recording, erasing and reproducing information by irradiating a laser beam,
On the substrate, a recording layer, an upper heat-resistant protective layer, an optical reflection layer is sequentially laminated, this heat-resistant protective layer is a hard carbon film containing carbon atoms and hydrogen atoms as main constituent elements,
An information recording medium characterized in that the recording layer contains a phase change type recording material represented by the following general formula as a main component. General formula Ag _α In _β Te _γ Sb _δ However, 5 ≦ α ≦ 22 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 instead of a hard carbon film containing carbon atoms and hydrogen atoms as main constituent elements. .. 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 velocity of 1.2 to 1.4 m / sec. An information recording method characterized by recording a signal.