DD298446A5 - OPTICAL RECORDING MEDIUM AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The present invention relates to an optical recording medium comprising a recording layer on a substrate and a protective film on a light reflection side and / or a light transmission side of the recording layer, wherein the protective film contains at least Si, Cr and N. The atomic ratio of Si and Cr in the protective film is Si1xCrx, where x is in the following range: 0.050.4. The optical recording medium can prevent a tarnish of a protective film and enlarge the protective effect of the protective film. It has an optical magnification effect due to the chromium content. {Recording medium, optical; Recording layer; Protective film; Information processing; Magneto-optics; Kerr effect; Light reflection; Light transmission; Alloy target}

Description

For this 1 page drawings

Field of application of the invention

This invention relates to an optical recording medium containing a recording layer and a method of manufacturing the optical recording medium. More particularly, this invention relates to an optical recording medium containing a protective film which does not cause film breakage, has an excellent optical magnifying effect, and has an excellent protective function for the recording layer. In particular, this invention also relates to a process for producing an optical recording medium having such a protective film having a high working efficiency for the film precipitate.

Characteristic of the known state of the art

Among the optical recording mediums with which the recording of information on the recording layer and the reproduction of the recorded information thereof by the application of an energy beam such as laser and the like are performed, an optical recording medium such that it only reproduces information Compact disc (CD) and CD-ROM, an optical recording medium such that information is recorded only once which is capable of recording but can not erase information, and an optical recording medium of the kind that information can be re-recorded frequently , In recent years, the optical recording medium of the kind that can be re-recorded has become particularly attractive since this system has the advantage that information can be re-recorded frequently. As the optical recording medium of this kind, a magneto-optical recording medium having a magneto-optical recording layer having a uniaxial magnetic anisotropy perpendicular to a film surface of a film constituting the recording layer and a phase change optical recording medium having a phase change between an amorphous one was developed and a crystalline state.

In the magneto-optical recording medium, a laser light is irradiated on the recording layer, resulting in a rotation of a polarization plane of the transmission or reflection light due to the magnetization state (size

and / or direction) at the irradiated area. Thus, by using its phenomenon (Kerr effect and / or Faracly effect), the magneto-optical recording medium makes it possible to reproduce information. To make the information reproducing apparatus compact, it is presently preferred to use the magneto-optical recording medium of the type which reproduces the information using the Kerr effect, since it is easier to determine a rotation angle (Kerr rotation angle) in the polarization plane of the reflection light. The larger the Kerr rotation angle, the less is the readout error at the time of information reproduction; therefore, various attempts are directed to increasing the Kerr rotation angle.

For example, Japanese Patent Publication No. 56-156943 discloses interposing a protective film between the magneto-optical recording film and the transparent substrate, this protective film containing a transparent dielectric film serving as a magnifying film for increasing the Kerr effect. This achieves an apparent increase in the Kerr rotation angle. It is known that the material forming the protective film contains a transparent dielectric film serving to increase the Kerr effect of an oxide such as ZrO ₂ , TiO ₂ , Bi ₂ O ₃ and SiO ₂ , as well as is made of a non-oxide such as CdS, Si ₃ N ₄ , AlN, SiC and ZnS. The transparent dielectric film of a non-oxide is better in the protective effect in comparison with the oxide film in order to increase the resistance to oxidation and corrosion. It is assumed that this film is used as the protective film. However, even if the transparent dielectric film containing Si ₃ N ₄ has a sufficient function as a protective film, it still has the disadvantages that the refractive index is 1.8 to 2.0 and less than the value of the dielectric film forming layer Material of the other non-oxide system (ZnS, CdS, SiC or the like), and the magnification effect of the Kerr effect is small.

To cope with these problems, the art has been developed that the thin transparent dielectric film comprising a main component of silicon nitride (Si ₃ N ₄ ) and a third component of an element such as Ti, Zr, Mo or the like, contains, as a protective film is used, which increases the Kerr effect, as described in Tier Japanese Patent Publication No. 61-22458, which corresponds to the US-PS 4680742 and 4851096. However, when the transparent dielectric thin film containing Si ₃ N _{4 is} stacked on the substrate together with the element (s) as the third component and used as a protective film which increases the Kerr effect, there was the possibility of That film cracks are caused and that the protective effect for the recording layer has become low.

In addition, the following methods have heretofore been used to deposit a magnifying layer of such a composition on the substrate: a method which uses co-evaporation of a Si ₃ N ₄ target and an alpha element target; a method using vapor deposition of a composition target, wherein the alpha-element chips are on the Si ₃ N ₄ ; a method which uses reactive co-vapor deposition of an Si target and an alpha element target; and a method which uses reactive vapor deposition of a composition target, wherein the alpha element chips are on the Si target. When the Si ₃ N ₄ target is used, however, the electrical insulating property of the Si ₃ N _{4 is} high, and when the Si target is used, a specific electrical resistance of Si is high, and an insulating thin film is deposited on the Si Target surface deposited in the case of reactive evaporation. It was therefore essential to use radio frequency (RF) vaporization and it was impossible to use direct current (DC) vaporization. DC vapor deposition is superior in film deposition rate and in film precipitation in comparison to RF vapor deposition. A film deposition technique for the protective film based on DC vapor deposition should be developed. The above-described disadvantages of the prior art have been successfully eliminated by this invention.

Object of the invention

It is an object of this invention to provide an optical recording medium whose protective layer has high resistance to corrosion, high magnification effect, and kink cracking. Another object of this invention is to propose a method of manufacturing the optical recording medium with which such a protective film can be formed on a substrate and / or a recording layer with a high efficiency using DC reactive vapor deposition ,

Explanation of the essence of the invention

The object of this invention is achieved by an optical recording medium containing a recording layer on a substrate and a protective film on a light reflection side and / or a light transmission side of the recording layer, the protective film containing at least Si, Cr and N.

It is preferable that the atomic ratio of Si and Cr contained in the protective film is represented by Si |. _x Cr _{x is} shown, where χ lies in the following range: 0.05 ^ x ^ 0.4.

The optical recording medium of the present invention can prevent a crack of a protective film and increases the protective effect of the protective film as well as an optical magnification effect because the protective film contains Cr other than Si and N. The object of the present invention is also achieved by a method of manufacturing the optical recording medium by forming such a protective film on a light-reflecting side and / or a light-transmitting side of the recording layer formed on the substrate by forming an alloy target of Si and an element is selected from the group consisting of a metal element, semimetal element, and a semiconductive element having a lower specific electrical resistance than Si, preferably an alloy target of Si and Cr as a cathode and used in a mixed gas atmosphere contains at least inert gas and N ₂ -GaS using DC magnetron sputtering. The alloy, for example, the Si-Cr target, makes it possible to use reactive DC evaporation, which was not used to form a silicon nitride film. As a result, high performance in forming a protective layer is achieved.

-3- 298 Execution examples

The invention and advantageous embodiments and modifications of the invention will be explained in more detail below in connection with the figures. It shows

1 shows a section through an embodiment of the optical recording medium according to the invention; and Fig. 2 is a sectional view of another embodiment of the optical recording medium of the present invention.

As shown in Fig. 1, an optical recording medium 1 according to the present invention has, for example, a structure.

wherein a protective film 3 and a recording layer 4 are laminated on a substrate 2 in the order mentioned. The optical recording medium according to the invention may, for example, another

Having a structure in which a protective film does not exist between the substrate 2 and the recording layer 4, but only on the Surface of the recording layer 4 is formed. It may also have a structure in which a protective film 3, a Au 'drawing layer 4 and a protective film 3 are successively stacked on the substrate 2. A Reflection layer 5 and / or a highly thermally conductive layer may be applied to the surface of the recording layer 2 as shown in FIG Fig. 2, or formed on the protective film formed on the recording layer. In the embodiments of Figs. 1 and 2, the optical recording medium is shown, which is designed so that

an energy beam, for example a laser beam, is incident from the direction of the arrow A, and a change in the optical

Property of the reflected light in the opposite direction is measured. In these embodiments, the serves Protective film located between the substrate 2 and the recording layer 4 as a magnifying layer around the Change the optical property also increase. The material of the substrate 2 is not limited to a specific material, but a transparent material is preferable. Both inorganic materials, such as glass or aluminum, and organic materials, such as polymethylmethacrylate, Polycarbonate, polymer alloy of polycarbonate and polystyrene, ethylene-cycloolefin copolymer, such as those described in U.S. Pat U.S. Patent 4,614,778, including copolymers of ethylene with 1,4,5,8-dimethano-1,2,3,4,4a, 5,8,8a-

octahydronaphtha'in (tetracyclododecene), copolymers of ethylene with 2-methyl-1,4,5,8-dimethane-1,2,3,4,4a, 5,8,8-octahydronaphthaiine (methyltetracyclododecene) and copolymers of ethylene with 2-ethyl 1-1,4,5,8-dimethane-1,2,3,4,4a, 5,8,8-octahydronaphthalene (ethyltetracyclododecene), poly-4-niethyl-1-pont, epoxy resin, polyetheisulfone, Polysulfone, polyetherimido, ethylene-tetracyclododecene copolymer are used as the substrate.

The material of the recording layer 4 is not limited to a specific material. But if the recording layer

is a magneto-optical layer, it is preferable that the recording layer (a) contains at least one element selected from the 3d transition metals, and (b) contains at least one element selected from the rare earth metals or (a) at least one element which is selected from the 3 d transition metals, (b) at least one

Contains element selected from the rare earth metals, and (c) contains metals related to corrosion

are resistant.

For the 3d transition metal, Fe, Co, Ti, V, Cr, Mn, Ni, Cu or Zn are used. Fe, Co or both are preferred. The Metals that are resistant to corrosion increase the resistance of the recording layer to acid. Pt, Pd, Ti, Zr, Ta, Mo, Nb or the like are used as the metal which is resistant to corrosion. Pt, Pd or Ti

are preferred and Pt, Pd or both are more preferred.

Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, Ce, Pr, Nd, Pm, Sm or Eu are used as the rare earth metal, and Gd, Tb, Dy Ho, Nd, Sm or Pr are preferred. When the recording layer is a layer other than a magneto-optical recording layer, e.g. Legs Phase change recording layer, it is made of a thin alloy film including Te or Se as one Main component, a thin Te-Ge-Sb alloy film, a Te-Ge-Cr thin alloy film, a Te-Ge-Zn thin film Alloy film, a thin In-Sb-Te alloy film or the like formed. The material of a reflection layer 5, which is represented by Fig. 2, is also not limited to a particular material. By way of example, a nickel alloy with a thermal conductivity of 2 J / cm · sec · K, the thermal Conductivity is 0.71 J / cm · sec · K, Pd whose thermal conductivity is 0.76J / cm K, Ti, whose thermal conductivity

0.22 J / cm sec K, Co whose thermal conductivity is 0.99 J / cm · K, Zr whose thermal conductivity is 0.23 J / cm · sec · K, and an alloy of these metals.

For the highly thermally conductive layer, an Al alloy is used, for example an Ai-Hf alloy, Al-Hf-Ti. Alloy, Al-Cr-Ti Alloy, Al-Nb Alloy, Al-Cr-Hf Alloy, Al-Ti-Nb Alloy, Al-Mg-Hf Alloy, Al-Mg-Ti Alloy, Al-Mg-Nb alloy, Al-Mg-Ti-Hf alloy and Al-Mg-Cr alloy. The amounts of metals except Al in these Alloys are preferably 10 atomic% or less. The protective film of the optical recording medium of the present invention is composed of a thin film which

contains at least Si, Cr and N. The atomic ratio of these elements is represented by the following formula:

wherein χ of the following formula satisfies 0.05 <χs0.4, preferably 0.1 Sx <0.3, and wherein y satisfies the following formula 0 <y <0.9, preferably 0.01 <y <0.9, mohr preferably 0.2 £ y <0.57. A protective film containing Si, Cr and N in this range has a high protective effect, does not crack, and has a higher optical magnifying effect than a protective film containing no Cr. In addition, the protective film enables the formation of the layer using the reactive DC evaporation, which was not used for the formation of a thin silicon nitride film containing no Cr. As a result, a great advantage in working performance in forming the protective layer is achieved. The recording layer 4 according to the invention has a thickness of preferably 50 to 5000 angstroms, preferably from 100 to 2000 angstroms. The protective film 3 according to the invention has a thickness of preferably 50 to 5000 angstroms, more preferably 100 to 3000 angstroms.

The method for producing the protective film 3 on the substrate 2 or the recording layer 4 will be described below

described. The protective film according to the invention can by reactive vapor deposition (reactive RF vapor deposition, reactive

DC evaporation) of a composition target, wherein Cr chips are on a Si target, or an Si-Cr alloy star

are formed in an atmosphere of a gas mixture consisting of acs inert gas and N ₂ . It is preferred that the

Protective film by reactive vapor deposition of an alloy target of Si and a metal, which has a lower relative

having electrical resistance, e.g. Cr, in an atmosphere of mixed gases consisting of inert gas and N ₂ , wherein the reactive vapor deposition is preferably by applying direct current (DC). Reactive DC vapor deposition survives RF vapor deposition in terms of film deposition rate and performance. As an inert gas He, Ne,

Ar, Kr or the like used, with Ar being preferred. According to the method of the invention, stable DC vapor deposition is performed by using an alloy target of Si and Cr or the like is used. This may be due to the fact that a glow discharge is stabilized when the Metal is contained in the target, which has a lower specific electrical resistance. The gas ratio of inert gas and N; reactive vapor deposition to make a protective film is 9: 1 to 0: 1,

preferably 7: 3 to 2: 8.

A recording layer 4 is formed on the protective film 3 formed on the substrate in an embodiment thereof Invention formed. According to the invention, the protective film 3 is likewise formed on a recording layer A ₁ on the substrate 2

is formed, or also formed on a recording layer 4, which is formed on the substrate, which thereon one

Protective film 3 contains. In addition, a reflection layer may be formed on the surface of the recording layer or the Protective film will be re-formed. According to the invention, there is available an optical recording medium containing a protective film comprising a

excellent optical magnification effect, has a high corrosion resistance and does not cause cracking since it contains Cr in addition to Si and N in its protective film. According to the invention, the protective film can be formed on a recording layer or a substrate by using DC reactive vapor deposition, which heretofore could not be used to form a thin Si-N film containing no Cr, because an alloy target such as Si -Cr, as one

Cathode is used. As a result, the power efficiency is greatly improved. Hereinafter, this invention will be described in more detail with reference to the following examples. The invention is

however, in no way limited to these examples.

example 1

A protective film containing Si, Cr and N and having a thickness of about 1000 angstroms was formed on an ethylene-tetracyclododecene copolymer substrate by reactive evaporation of a composition target in which Cr chips are disposed on the Si target. with an impressed RF500-W power and in an atmosphere of mixed gases of Ar 20SCCM and N ₂ 20SCCM (1.5m Torr). The atomic ratio of Si to Cr was 67:33. Next, a recording layer of Tb-Fe-Co with a thickness of about 1000Angström was χ on the protective film by a DC magnetron coating at 20 to 50 ° C and 1.0 10 ^"7 Torr in an Ar atmosphere formed. A The optical recording medium was obtained by forming a protective film of Si-Cr-N having a thickness of about 1000 angstroms on the recording layer by the same method as described above 85 ° C and a relative humidity of 85% The coercive force did not change during this experiment.

An optical constant and the result of the tearing test of this protective film are shown in Table 1. The optical constant of this protective film was measured by means of an ellipsometer (at a wavelength of 839 nm). The tearing test of the protective film formed on the substrate was performed before the recording layer and a protective film were successively formed.

Table 1

refractive index Black-Out example 1 2.2 O Example 2 2.2 O Example 3 2.2 O Comparative Example 2 2.2 X Comparative Example 3 2.2 X Comparative Example 4 2.0 X Comparative Example 5 2.1 X Comparative Example 6 1.9 X Comparative Example 7 2.2 X Comparative Example 7 2.2 X

ο means that no cracks were observed, χ means that some cracks occurred in the layer.

Example 2 An optical recording medium was obtained by using protective films of Si-Cr-N both on the substrate and on the substrate Recording layer was formed by the same method as described in Example 1, except that a Sintered alloy target of Si and Cr (Cr 20 at%) was used as a cathode. The atomic ratio of Si to Cr in the Protective films was 80:20. The coercive force (Hc) did not change during the life test comparatively as in Example 1. An optical Constant of the protective film as well as the result of the tearing test are also listed in Table 1. reference example Before preparing an optical recording medium, the following experiments were conducted after the reactive DC steaming is necessary.

Trial 1:

After evacuating the chamber to less than 5 × 10 ^"6 torr, the reactive DC sputtering with imposed DC 300 W was performed 20 SCCM in an atmosphere of mixed gases of Ar gas 20 SCCM and N ₂ gas, wherein an alloy target of Si and Cr (composition: Si ₈ OCr ₂ O, size 4 inches [10.16 cm]) It was found that the glow discharge was stable under this condition.

Trial 2:

After the pressure of Kamr. he injecting air at atmospheric pressure, and then was divided again to less than 5 x 10 ~ ^B Torr, was again performed next, the reactive DC sputtering in a similar manner as in the method described above. Again, it was found that the glow discharge was stable.

Example 3 After evacuating the chamber to less than 5 x 10 ^-6 Torr, the reactive DC sputtering with imposed DC 300W was in

one atmosphere (1.5m Torr) of mixed gases of Ar gas 20SCCM ur d N ₂ -GaS 20SCCM performed using a

Alloy target of Si and Cr (composition: Si ₈₀ Cr ₂ O, size 4 inches (10.1 Bern)) was used as a cathode to

to deposit a protective film of Sci-Cr-N on an ethylene-tetracyclodecene copolymer substrate, this

Protective film had a thickness of about 10OOAngströ η. Next, by DC magnetron sputtering alloy targets of sines Tc-Se-Co χ at 20 to 50 ° C and 1.0 10 ^-7 Torr

In an Ar atmosphere, a recording layer of Tb-Fe-Co having a thickness of about 1000 angstroms is formed on the protective film. Then, an optical recording medium was obtained by coating a protective film of Si-Cr-N with a

Thickness of about 1000 angstroms was formed on the recording layer in a similar manner as described above. The atomic ratio of Si to Cr in the protective film was 80:20. It was found that the glow discharge was stable during the deposition of the protective film. The coercive force (Hc)

did not change during the life test similar to Example 1. An optical constant of the protective film as well as the result of the tearing test are also listed in Table 1.

Examples 4 to 9 An optical recording medium was obtained by the same method as in Example 3 except that the flow rate of the

mixed gases of Ar and N _{2 was} varied.

The flow rate of the gases, the rate of formation and the optical constant of the protective films are listed in Table 2. Table 2

target power Gas (SCCM) N ₂ film deposition refraction Movie (W) Ar 20 impact rate index crack Example 4 Si ₈₀ Cr ₂₀ DC 300 20 105 2.2 O (Alloy target) 4 Examples ditto. DC300 36 12 128 3.7 O Examples ditto. DC300 28 16 121 2.7 O Example 7 ditto. DC300 24 24 109 2.3 O Examples ditto. DC300 16 28 97 2.3 O Example 9 ditto. DC300 12 72 2.2 O

ο means that no crack was observed.

Comparative Example 1 The formation of a protective film was attempted by using only a Si target as the cathode under the same condition as in Example 3 was used. However, the discharge was not stable and the protective layer could not be formed. Comparative Example 2

An optical recording medium was obtained by forming protective films on both the substrate and the recording layer under the same condition as in Example 1, except that a composition target of a Si target having Mo chips disposed thereon were, was used. The result is shown in Table ¹ .

Comparative Example 3 An optical recording medium was obtained by using protective films on both the substrate and the substrate Recording layer under the same condition as in Example 1 were formed, except that a Composition target from a Si target with Nd chips was used. The results are in Table 1

specified.

Comparative Example 4

An optical recording medium was obtained by forming protective films on both the substrate and the recording layer under the same condition as in Example 1, except that a composition target of a Si target with Tb chips was used. The results are shown in Table 1.

Interrelated Explanatory 5

An optical recording medium was obtained by forming protective films on both the substrate and the recording layer under the same condition as in Example 1, except that a composition target of a Si target having Gd chips was used thereon. The results are given in Table.

Verglelchsbelsplel 3

An optical recording medium was obtained by forming protective films on both the suister and the recording layer under the same condition as in Example 1, except that a composite target of a Si target with co-chips was used thereon. The results are given in Table.

Vergloichsbelsplel 7

An optical recording medium was obtained by forming protective films on both the substrate and the recording layer under the same condition as in Example 1, except that e. > Composition target from a Si target with Ti chips was used on it. The atomic ratio of Si. * Ti in the protective film was 69:31. The results are shown in Table 1.

Comparative Example 8

An optical recording medium was obtained by forming protective films on both the substrate and the recording layer under the same condition as in Example 1, except that a composition target of a Si target having Zr chips was used thereon , The atomic ratio of Si to Zr in the protective film was 92: 8. The results are shown in Table 1.

It is found that in the protective films according to Examples 1 to 3, the cracking occurs less than the protective films according to Comparative Examples 1 to 8 that they have high refractive power and that they are used either as a protective film or as an optical magnification layer.

Claims (7)

An optical recording medium, characterized in that it consists of: a substrate; a recording layer disposed on the substrate; and a protective film disposed on a light reflection side and / or a light transmission side of the recording layer, wherein the protective film contains at least Si, Cr and N. 2. An optical recording medium according to claim 1, characterized in that the atomic ratio of Si to Cr contained in the protective film is represented by Si ₁ -XCr _x , where χ satisfies the equation 0.05 <x <0.4. The optical recording medium according to claim 1 or 2, characterized in that the recording layer is composed of a magneto-optical recording layer having a uniaxial magnetic anisotropy perpendicular to a film surface of a film forming the recording layer. 4. An optical recording medium according to any one of claims 1 to 3, characterized in that the recording layer consists of a thin film containing a recording material, which is variable in terms of an optical property, for example, the reflection and / or transmission factor. 5. A method for producing an optical recording medium having a recording layer and a protective film on the substrate, characterized by forming a cathode consisting of an alloy target of Si and at least one element selected from the group consisting of a metal element, semimetal element and a semiconductive element having a lower specific electrical resistance than Si; and Performing DC magnetron sputtering in an atmosphere of mixed gases containing at least one inert gas and N ₂ -GaS to form a precipitate of the protective film. 6. The method according to claim 5, characterized in that the protective film is deposited on a light reflection and / or light transmission side of the recording layer. 7. The method according to claim 5 or 6, characterized in that the element having a lower electrical resistivity than Si Cr.