JPH0896414A - Optical element, information recording medium, and information recording / reproducing apparatus - Google Patents

Abstract

(57) [Summary] [Structure] An optical reflection layer 24 such as an optical disk such as a compact disk or a laser disk or a magneto-optical recording medium (MO disk), a phase change recording medium, a write-once alloy recording medium, a write-once dye recording medium, or the like is provided. , A plurality of layers of a first layer (thin film M1) and a second layer (thin film M2) having different compositions or textures (preferably two or more layers are alternately laminated alternately)
And the first and second layers (thin film M
The thicknesses of 1 and M2) are each 0.2 nm or more, which is approximately the size of one atom, and 20 nm or less, which is approximately the size of a crystal grain. [Effect] The grain boundary becomes discontinuous at the boundary surface between the first layer and the second layer. Therefore, the progress of corrosion along the grain boundaries is suppressed, and as a result, the reflectivity of the light-reflecting layer is maintained well without change over time, and as a result, the reproducing function is guaranteed with high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element having at least a light reflecting layer formed on a substrate, an information recording medium and an information recording / reproducing apparatus.

[0002]

2. Description of the Related Art As an optical (or information) recording medium for reproducing information using a light reflecting film, for example, an optical disc such as a CD (compact disc) or an LD (laser disc) is known as shown in FIG. ing.

In this optical disc 1, PMMA
Irregularities (pits corresponding to signals) 3 are formed on a transparent substrate 2 made of (polymethylmethacrylate) or PC (polycarbonate), and a metal film that reflects light (usually about 0.1 μm thick) is formed on the surface including these pits. Al film) 4 is provided, and a protective film 5 is further provided on the entire surface with signal pits 3 and a reflective film 4.
It is provided to protect the.

To reproduce recorded information using such an optical disk, in the recording / reproducing apparatus shown in FIG. 17, the semiconductor laser light 7 from the semiconductor laser 6 is collimated by the collimator lens 8 and condensed by the objective lens 9. Then, the information is made incident on the optical disc 1 from the transparent substrate 2 side, transmitted through the transparent substrate 2 and reflected light from the light reflection film 4 changes the unevenness information of the pits 3 of the signal layer into a light amount change using light interference. Then, the reflected light 10 is sent to the photodiode 11 and detected. In FIG. 17, reference numeral 12 is a beam splitter for separating the reflected light 10 from the laser light (incident light) 7.

As described above, since the reflection information of the pit is detected and reproduced by the reflected light, the characteristic of the reflected light is important. The characteristic of the reflected light is the light reflection film (4 in FIG. 16). Greatly depends on the stability of (corrosion resistance).

Generally, the light reflecting film is made of, for example, aluminum or its alloy and is formed by a vacuum deposition method or the like. The film quality is a polycrystalline film as shown in the TEM (transmission electron microscope) photograph of FIG. ing. This photograph shows a transmission electron microscope image of an aluminum film on a polymethylmethacrylate substrate after the protective film of the aluminum film and the substrate were dissolved and removed with a solvent.

In CDs, LDs, etc., reliability is obtained by adding impurities to the aluminum film and forming a protective film for preventing oxidation (corrosion) of the aluminum film. However, it is a problem that the polycrystalline film as shown in FIG. 18 includes grain boundaries (boundaries between crystal grains).

That is, RA Vandermeer and P. Gordon;
Edge-Nucleated, Growth Controlled Recrystallizatio
n in Aluminum, Trans.AIME. 215, Aug. (1959), p.57
As shown in 7., in the experiment of high-purity aluminum with a workability of 40%, it is recognized that the recrystallized grains of aluminum develop from the grain boundaries (grain boundary triple points) of three grains. Recrystallization of aluminum causes hillocks, which greatly deteriorates the flatness of the aluminum film and deteriorates reliability (see Japanese Patent Laid-Open No. 62-137743). In addition, the progress of corrosion (diffusion) at grain boundaries is much faster than the progress within crystal grains, and there are problems such as accelerated deterioration of the aluminum film (change in light reflectance) (aluminum processing technology). See Handbook, P102, (2) Intergranular corrosion).

In such an aluminum polycrystal film, oxidation (corrosion) progresses rapidly from the crystal grain boundaries.
Characteristics such as corrosion resistance deteriorate with time.
Due to this change over time, as shown in FIG. 19, the state of the reflected light 10 changes, and the reproduction signal characteristics deteriorate. This is particularly noticeable when high density recording and reproduction with short wavelength light are performed.

As a method for improving the reliability of an aluminum film, as disclosed in JP-A-62-137743, by adding an alloying element such as titanium to aluminum, the corrosion of the aluminum alloy film and the aluminum alloy film are prevented. Recrystallization (hence hillock generation) can be considerably suppressed. However, even in an optical disc using such an aluminum alloy film as a light-reflecting film, corrosion progresses from the grain boundaries. Therefore, when subjected to an accelerated deterioration test performed under high temperature and high humidity conditions, the stability of the light-reflecting film is shown. (Characteristics over time) gradually deteriorate.

[0011]

An object of the present invention is to provide an optical element such as an optical disc or an information recording medium which has good aging characteristics such as hillock resistance and corrosion resistance and can greatly improve reliability, and further, An object is to provide an information recording / reproducing apparatus using this.

[0012]

That is, according to the present invention, a base (for example, a transparent glass substrate 2 described later) and a light reflection layer (for example, a light reflection film 4 or 24 described later) provided on the base are provided. In the optical element, the light reflection layer is composed of a laminated film composed of at least two kinds of layers having different compositions and / or structures, and the thickness of each of the at least two kinds of layers is 0.2 nm. The optical element having a thickness of 20 nm or less.

In the present invention, it is desirable that at least the first layer and the second layer are alternately laminated two or more times to form the light reflecting layer.

Further, in the present invention, at least the first layer and the second layer can be made of elements, alloys or compounds (oxides, nitrides, carbides, etc.). For example, Au / Al, AgZn / CuZn, Al /
SiN, TiC / SiO, AlCu / NbB, Cu / M
It can be composed of gF, Au / SiN / AlN, or the like.

Further, in the present invention, in order to improve light reflection, at least one of the first layer and the second layer contains 50 atomic% or more of metal (for example, TiN / Si). ₃ N ₄ lamination) is desirable.

Further, in the present invention, at least the first layer and the second layer can be constituted by an epitaxially grown structure, a polycrystalline structure, an amorphous structure or a mixed structure thereof. For example, Au, A of uniform composition
Whether it is an element 1, AgZn alloy, or an amorphous material such as AuSi or CuZr, different face-centered cubic (FCC) compositions such as Ag ₄₀ Fe _{60 having} a high Ag content and a body-centered cubic lattice (B
It may be composed of two or more different compositions such as a mixture of two kinds of CC) having a large amount of Fe, and a crystal structure.

Further, in the present invention, incident light, particularly light having a wavelength of 100 nm or more is used as recording / reproducing light.

Further, in the present invention, the light reflecting layer can be constructed so that the composition of these layers is rapidly changed at least at the interface between the first layer and the second layer.

In the present invention, at least one of the first layer and the second layer has a second phase (for example, a dispersed phase M described later) in a first phase (for example, a mother phase M3 described later).
The light-reflecting layer can be configured to have a structure in which 4) is dispersed.

Further, in the present invention, at least one of the first layer and the second layer is divided with a gap (for example, a gap D described later) in the surface direction, and the interlayers on both surfaces are separated in this division region. The light-reflecting layer can be configured to be connected.

In the present invention, an intermediate layer in which the composition continuously changes from the composition of the first layer to the composition of the second layer between at least the first layer and the second layer. (For example, a composition gradient film M5 described later) is interposed, and the light reflection layer can be configured so that the intermediate layer does not cause a sudden change in composition.

In the present invention, at least the first layer and the second layer have mutually different functions (for example, in addition to the high reflectance layer, corrosion resistance and thermal conductivity (copper film The light-reflecting layer can be configured as a (preferred) layer or a protective layer).

Further, in the present invention, at least the first layer and the second layer can be formed by a sputtering method, a vapor deposition method (including molecular beam epitaxy (MBE)), a CVD method or a plating method. .

In the present invention, the surface of the light reflecting layer opposite to the substrate may be covered with a protective layer (for example, protective film 5 described later).

Further, according to the present invention, one or both of the surface of the light-reflecting layer on the side of the substrate and the surface on the side of reflecting the substrate,
It can be covered by a dielectric layer.

Further, in the present invention, a recording layer on which a predetermined signal is recorded or which can be recorded (for example, a magnetic layer 2 described later).
5, a phase change layer, a write-once type alloy layer, a write-once type dye layer, etc.) is formed, and a light reflection layer is provided directly on this recording layer or via a dielectric layer to form an optical element (that is, a magneto-optical element). Recording optical element, phase change recording optical element, write-once alloy recording optical element,
A write-once dye optical element or the like) can be used.

The present invention is also an information recording medium having at least a light-reflecting layer formed on a substrate so as to record predetermined information, wherein the light-reflecting layer is one of the above-mentioned light-reflecting layers. The present invention relates to an information recording medium characterized by comprising:

The present invention also relates to an information recording / reproducing apparatus configured to record / reproduce predetermined information by arranging any one of the above optical elements in an optical system.

As an optical element having a laminated structure, a soft X-ray having a wavelength equal to or shorter than 30 nm in the soft X-ray region and having the same wavelength as the lamination period of the laminated film is used.
A laminated film of Si / Mo, C / W, BN / Mo, etc. made of a combination of a heavy metal film and a light element film as a laminated film that strongly reflects soft X-rays by utilizing the interference caused by laminating rays. It has been known. Such an optical element is used at an X-ray wavelength depending on the lamination period of the reflection film, and the X-ray wavelength is 30 nm.
Below is a short one.

On the other hand, in the present invention, the light reflecting layer is different from the above X-ray reflecting film depending on the stacking period.
The wavelength of the light used is from ultraviolet light of 100 nm or more to infrared light, and it is a pure light reflection layer that reflects incident light.

[0031]

In the present invention, the reflecting layer has a laminated structure composed of the first and second layers, and the size of the crystal grains of each of these layers is limited by the thickness of the first and second layers. The crystal grain boundaries are made discontinuous at the first and second interfaces so that it is difficult to include crystal grain boundaries that are long and continuous in the depth direction, and corrosion (oxidation) that progresses from the crystal grain boundaries is suppressed.

The thickness of each single layer of the first and second layers is
If it is less than 0.2 nm, the thickness becomes one atomic layer or less, and it becomes impossible to distinguish between the first and second layers in the same manner as a diffused state. Also, when this exceeds 20 nm, the size of the crystal grains becomes almost the same as the size of the crystal grains when only a single layer is formed, and the crystal grains are laminated in the first and second layers. You can no longer be restricted.

[0033]

Embodiments of the present invention will be described below.

FIG. 2 is a schematic sectional view of a part of an optical disc according to the present invention. The optical disc 21 is PMMA (polymethylmethacrylate) or PC (polycarbonate).
Minute irregularities (pits corresponding to signals) 3 are formed on a transparent substrate 2 made of, and on the surface including these pits 3,
A light reflection layer 24 that reflects light is provided. On the light reflecting layer 24, a protective layer 5 (shown by a virtual line) for protecting it may be provided.

The light reflecting layer 24 has a laminated structure in which two kinds of thin films M1 and M2 are alternately laminated, as shown in an enlarged partial sectional view of FIG.

The light-reflecting layer shown in FIG. 1A is a thin film M composed of a single phase or a plurality of phases and having different compositions and / or structures.
The light reflection layer 24 is formed by alternately laminating 1 and M2.

In the light reflection layer shown in FIG. 1B, a thin film M2 composed of a single phase or a plurality of phases and a thin film M1 having a structure in which a second phase M4 is dispersed in a first phase M3 are alternately arranged. To form a light reflection layer 24. The thin films M1 and M2 have different compositions and / or structures.

In the light reflection layer shown in FIG. 1C, the thin film M2 is divided in the plane direction with a gap D in between, and the thin film M1 located with the thin film M2 interposed therebetween fills the gap D and is located at this position. It has a connected structure.

In the light reflecting layer shown in FIG. 1D, a composition gradient film M5 having a composition which continuously changes from that of the thin film M1 to that of the thin film M2 is arranged between the thin films M1 and M2. It has a structure. With such a structure, the adhesiveness of each thin film is improved without abrupt changes in composition.

The light-reflecting layer is composed of (a), (b), (c) or (b), (c) in FIG. 1 (a)-(d).
It is also possible to have a laminated structure in which any two or three kinds such as (d) are combined.

An RF (radio frequency) and DC (direct current) magnetron sputtering apparatus provided with four targets was used for forming each thin film. For these targets, the supply power can be adjusted independently with respect to the necessary target element, alloy, or compound target. Sputtering was performed by using a necessary target under a condition of an argon gas pressure of 0.4 Pa after the inside of the apparatus was set to a vacuum degree of 10 ⁻⁴ Pa. The laminated film thickness was controlled by adjusting the power of the target, the rotation speed of the substrate, and the sputtering time.

Example 1 In this example, the light reflection layer 24 has the structure shown in FIG. 1A, the thin film M1 is an aluminum film, and the thin film M2 is a titanium film. And 1
The thickness of the thin film M1 is 0.75 nm, and the thickness of the thin film M2 is 0.3 nm
As a result, the total thickness of the light reflection layer 24 is 280 nm.
There is. The thin film in direct contact with the substrate 2 is aluminum, and the uppermost thin film is titanium.

As shown in FIG. 2, the light reflection layer 24 of the optical disk 21 may be covered with the protective layer 5, but in this example, the light reflection layer has corrosion resistance, hillock generation state, and crystal structure. In order to examine the stacking period and the stacking period, the following test was performed before the protective layer was not attached. Corrosion resistance and hillock generation are tested at temperature
Performed by high temperature, high humidity acceleration test at 60 ℃, relative humidity 85%,
The crystal structure and the stacking period were examined from the plane spacing by a Cu-Kα X-ray diffraction test (wavelength λ = 0.1542 nm).

A laminated film of 0.75 nm Al / 0.3 nm Ti having a total thickness of 280 nm was formed on a glass substrate by sputtering using an aluminum target and a titanium target and adjusting the power supply power and the substrate rotation speed.

As a comparative sample, a light-reflecting layer (Comparative Example 1-1) consisting of an aluminum single layer having a film thickness of 100 nm, a film thickness
A light-reflecting layer consisting of a 690 nm nickel single layer (Comparative Example 1-
2), a light-reflecting layer made of a titanium single layer having a thickness of 240 nm (Comparative Example 1-3) and a single layer of aluminum-titanium alloy having the same composition and the same thickness when the substrate rotation speed in Example 1 was 120 rpm. A light reflecting layer (Comparative Example 1-4) was produced.
Each of the comparative examples has a polycrystalline structure.

The results of the X-ray diffraction test for the light reflecting layer of Example 1 and the light reflecting layer of Comparative Examples 1-4 are as shown in FIG.

In the laminated light-reflecting layer of Example 1, a diffraction peak corresponding to a laminating period with a face spacing d = 1.12 nm was detected at 2θ = 7.9 degrees, and the crystal structure of the entire layer was a face-centered cubic lattice (FCC).
Then, the lattice constant is 0.4025 nm. In the aluminum-titanium alloy film of Comparative Example 1-4, in the equilibrium state, aluminum and titanium form a solid solution of only about 1%.
(FCC, lattice constant a = 0.4049 nm), Ti (dense hexagonal lattice (HCP), lattice constant a = 0.2950 nm, c = 0.4686 nm)
A peak due to
No peak corresponding to titanium was detected. The alloy film has a single phase of FCC structure and its lattice constant is 0.3966 nm.
It was found to consist of an Al-Ti forced (supersaturated) solid solution.

Next, the results of the accelerated deterioration test for each light reflecting layer will be described with reference to optical microscope images (magnification: 200 times) shown in FIGS. Each of (a) in these figures shows the structure immediately before the start of the test, and each is a film having a metallic luster and no defect.

In the light reflecting layer of Example 1, after the accelerated deterioration test for one month, as shown in FIG. 4 (b), no change was observed with respect to the initial state (FIG. 4 (a)).

In the aluminum single-layer light-reflecting layer of Comparative Example 1-1, as shown in FIG.
It is observed that corrosion progresses from the grain boundaries. It can be seen that the aluminum polycrystal film of this light reflection layer is mostly transparent.

In the nickel single-layer light reflecting layer of Comparative Example 1-2, as shown in FIG. 6B, a difference from the initial state (FIG. 6A) was observed only after 1 month, It has been found to exhibit relatively good corrosion resistance.

In the titanium single-layer light reflecting layer of Comparative Example 1-3, as shown in FIG. 7B, almost no difference from the initial state (FIG. 7A) was observed after one month. , Shows quite high corrosion resistance.

In the light-reflecting layer of the aluminum-titanium alloy single layer of Comparative Example 1-4, it is observed that small defects grow after one month as shown in FIG. 8 (b). However, even after the lapse of two months, the condition after the lapse of one month is generally maintained, and it is considered that a fairly high reliability is guaranteed in terms of corrosion resistance.

From the above test results, the light-reflective layer of Example 1 is the most reliable from the viewpoint of corrosion resistance.

Example 2 In this example, the light reflection layer 24 has the structure shown in FIG. 1A, the thin film M1 is an aluminum film, and the thin film M2 is a nickel film. And
The thickness of the thin film M1 is 2.4 nm, the thickness of the thin film M2 is 0.6 nm, and the total thickness of the light reflection layer is 340 nm. For film formation, using a sputtering device, after evacuating to 10 ^-4 Pa,
The target power of aluminum and nickel was adjusted with an argon gas pressure of 0.4 Pa, aluminum was sputtered with a sputter rate of 0.4 nm / sec, nickel was sputtered with a sputter rate of 0.1 nm / sec, and the rotation speed of the substrate was adjusted to 10 rpm. Was deposited.

As a comparative example, an aluminum-nickel alloy single layer light reflecting layer (Comparative Example 2) was formed by sputtering while making the entire composition the same as in Example 2. The film forming conditions were that the number of rotations of the substrate was 120 rpm, and other conditions were the same as in Example 2.

From the results of the X-ray diffraction test shown in FIGS. 9 and 10, the laminated light-reflecting layer of Example 2 had d = 2.
A diffraction peak due to a stacking period of 91 nm is detected, and the structure of the entire light reflection layer is a stack structure of an amorphous aluminum film (M1) and a fine polycrystalline nickel film (M2), and the nickel is a lattice. The FCC structure has a constant of 0.3528 nm.
In Figure 9, the broad peak around 2θ = 24 degrees is
Due to the glass of the substrate, aluminum (111 surface)
No clear peak was observed at the position of [2θ = about 38 °], indicating that the thin film M1 was made of amorphous aluminum. The peak near 2θ = 44 degrees is nickel (11
It corresponds to 1 side). The total thickness of the light reflection layer is 3
40 nm.

The light-reflecting layer of Comparative Example 2 had a mixed structure of amorphous aluminum and a phase thought to be fine crystals of nickel having an FCC structure, and the lattice constant of the nickel phase determined by X-ray diffraction was
0.3500nm (The value of nickel lattice constant in the constant table is 0.3524nm)
The average crystal grain size of the microcrystalline nickel obtained from the half-width of the diffraction peak at 2.1 nm is 2.1 nm. The film thickness of the light reflection layer is 340 nm as in the second embodiment. Since the lattice constant is small, it is presumed that compressive stress is applied to the nickel fine crystal grains.

The light-reflecting layer of Comparative Example 2 had a structure in which amorphous aluminum (which may contain a little nickel) and fine crystalline nickel or fine crystalline nickel containing a slight amount of aluminum as a solid solution were mixed. I found out that That is, the light-reflecting layer of this alloy has a structure in which nickel or fine crystals of a small amount of aluminum dissolved in nickel are scattered everywhere in the amorphous aluminum.

As a result of the accelerated deterioration test, the light reflecting layer of Example 2 showed no difference from the initial state (FIG. 11 (a)) after 1 month as shown in FIG. 11 (b). It can be understood that it shows high reliability. On the other hand, in the light-reflecting layer of Comparative Example 2, remarkable defect growth is observed as shown in FIG. 12B after one week from the initial state shown in FIG.

Example 3 In this example, the light reflection layer 24 has the structure shown in FIG. 1A, the thin film M1 is a silicon thin film, and the thin film M2 is a tungsten thin film. This laminated structure is a structure used for an X-ray mirror.
The thin film M1 has a thickness of 2.1 nm, and the thin film M2 has a thickness of
The thickness is 1.0 nm and the total film thickness is 600 nm.

The result of the X-ray diffraction test for this light reflecting layer is as shown in FIG. 2θ = 5.69 degrees, 8.49 degrees,
Diffraction peaks from the 2nd order to the 7th order due to the stacking period of d = 3.1 nm are detected at 11.3 degrees, 14.12 degrees, 16.89 degrees, and 19.77 degrees, and both the thin films M1 and M2 have an amorphous structure.

As a result of the accelerated deterioration test, the light reflecting layer of Example 3 showed a difference from the initial state (FIG. 14 (a)) only after two weeks, as shown in FIG. 14 (b). It can be understood that it shows extremely high reliability.

The results of the accelerated deterioration test for each of the above Examples and Comparative Examples are shown in the table below in association with the elapsed time. In the table, ○ indicates that the same state as during film formation is maintained, △ indicates slightly corroded spots, and × indicates that corrosion is progressing in a fairly wide area. There is.

[0065]

The laminated light-reflecting layers of Examples 1 and 2 showed almost no difference from the initial state after 2 weeks of high temperature and high humidity accelerated aging test, and a comparative example composed of a single layer of an alloy of the same composition. Very high reliability is obtained as compared with (Comparative Examples 1-4, 2).

As a comparative example with respect to Example 3, a high temperature and high humidity accelerated deterioration test on a tungsten single layer was not conducted. This is because metallic tungsten is known to be easily oxidized even in a moist atmosphere. Therefore, since the laminated light-reflecting layer of Example 3 was only slightly corroded in the high-temperature high-humidity accelerated test for one week, as in Examples 1 and 2, the tungsten film and the tungsten-silicon alloy were not corroded. It can be seen that it shows higher reliability than the membrane.

In all of the above examples, the film is formed by sputtering, but in addition to this, the film can be formed by vapor deposition, CVD or plating.

The light-reflecting layer based on the present invention is Japanese Patent Application No. 5-298890 previously proposed by the present applicant (a structure in which 50% or more of the effective area of the light-reflecting layer has no grain boundary).
Similarly, since the reliability is very high, sufficient reliability can be expected in the signal reproduction of the optical disc.

Example 4 Using a target of nickel and a Zr ₅₀ N ₅₀ compound, nickel was added in an argon gas.
C magnetron sputter and Zr ₅₀ N ₅₀ were RF magnetron sputtered, and each was alternately laminated 7 times with a thickness of 15 nm to obtain a 15 nm Ni / 15 nm ZrN light reflection layer with a total thickness of 210 nm. Z
rN had a bcc structure and a lattice constant of 0.458 nm.

Example 5 A target in which a silicon dioxide (SiO ₂ ) chip was mounted on a nickel target at an area ratio of 10% and a Si ₃ N ₄ compound target were alternately deposited by RF magnetron sputtering, and the deposition was repeated 10 times. Layered, total thickness 200nm
Of 15NmNi ₉₀ was obtained _{(SiO 2) 10 / 5nmSi 3} N 4 the light reflecting layer.

<Example 6> In the laminated light reflection layer of 0.3 nm Al / 0.6 nm Ti produced in the same manner as in Example 1, a lamination period of 0.9 nm is observed. This indicates that the light reflection layer has a laminated structure of a layer of 1 atom of aluminum and a layer of 2 atoms of titanium, and shows that the composition is rapidly changed at the lamination interface.

<Example 7> An Al ₈₀ Ni ₂₀ alloy target and a titanium target were used to perform DC magnetron sputtering of both targets alternately, and a total thickness of 200 nm was 15 nm Al _80.
To obtain a Ni ₂₀ / 10nmTi light reflective layer. In the Al ₈₀ Ni ₂₀ alloy layer, as in the aluminum-nickel alloy single layer of Comparative Example 2 described above, FC was added in the amorphous aluminum phase.
A composition in which nickel crystallites having a C structure were dispersed was observed.

Example 8 Using a Fe ₈₀ Ag ₂₀ alloy target and a silver target, a total thickness of 210 nm was 1 nm Fe ₈₀ Ag.
_A 20/20 nm Ag light reflecting layer was obtained. By subjecting this to heat treatment at 400 ° C., the Fe-Ag alloy phase becomes Fe phase and A
Since it is separated into the g phase and the Ag layers on both sides are connected via this Ag phase, it is divided as shown by M2 in FIG. 1 (c), and two layers of M1 (silver layer) are separated at this dividing point. It became a continuous composition.

Example 9 Using an Ni ₇₀ Zr ₃₀ alloy target, sputtering was performed while the argon gas pressure was kept constant at 0.4 Pa and the nitrogen gas pressure was changed in the range of 0 to 0.04 Pa as follows. First, sputtering is performed at a nitrogen gas pressure of 0 for 1 minute, then the nitrogen gas pressure is increased to 0.04 Pa over 30 seconds, this state is maintained for 1 minute, and the nitrogen gas pressure is returned to 0 over 30 seconds. This operation was repeated 5 times to obtain a total thickness of 300 nm for 10 nm Ni.
ZrNx / 20nm NiZrN / 10nm NiZrNx / 20nmN
An iZr light reflecting layer was obtained.

The light-reflecting layers of Examples 4 to 9 described above showed high reliability, with no change observed after 1 week of high temperature and high humidity accelerated deterioration test.

For example, in the laminated light-reflecting layer according to Example 5, the Ni ₉₀ (SiO ₂ ) ₁₀ film serves as a light-reflecting layer, and the Si ₃ N ₄ film transmits visible light, but the light-reflecting film ( That is, they each have a function as a protective film for preventing oxidation of Ni).

When forming the first layer and the second layer in the light reflection layer, the laminated light reflection layer can be obtained by vapor deposition while alternately controlling the shutter. Even in the CVD method, a laminated structure can be obtained by alternately switching the film forming gases. Similarly, in the plating method, it is possible to stack the layers by alternately changing the plating baths.

Further, one or both of the one surface and the other surface of the light reflecting layer is formed with SiN, SiO ₂ , Zn.
It may be covered with a dielectric layer such as S-SiO ₂ .

The above example is an example of an optical disc such as a compact disc or a laser disc, but a light reflecting layer according to the present invention can be provided on a magneto-optical recording medium (MO) or the like. FIG. 15 is an enlarged partial sectional view of the MO disk 41 having such a structure.

The transparent substrate 2 has a magneto-optical recording layer 25 and a light-reflecting layer.
24 and the protective layer 5 are applied in this order. The light reflection layer 24 has the laminated structure shown in FIG. 1, but this laminated structure is
It is omitted in FIG.

Since the reproduction signal of the magneto-optical recording medium (MO) is not only reflected from the magneto-optical recording layer 25 but also reflected from the light-reflecting layer 24, the characteristics are further improved. (For example, the reliability described above) becomes important.

Although the embodiments of the present invention have been described above, the above-mentioned embodiments can be variously modified based on the technical idea of the present invention.

For example, in the above-mentioned optical disc, the material, structure, or texture of the light-reflecting layer, the material of the transparent substrate or each disc-constituting layer may be changed variously. The condition of the structure or texture can be controlled by the formation or film formation conditions of the light reflecting layer.

Further, the present invention is similarly applicable to other media such as phase change media, write-once alloy media, write-once dye media and the like, in which the signal characteristics are improved by the light reflecting layer.

The present invention can be applied not only to the above-mentioned optical disk and the like, but also to other optical elements, for example, various mirrors including a tracking mirror arranged in an optical system. In addition to the signal reproduction system or device,
It is also applicable to a signal recording system or device, or a system or device having both functions.

[0087]

According to the present invention, the light reflecting layer is constituted by a laminated film composed of at least two kinds of layers having different compositions and / or structures, and the thickness of the at least two kinds of layers is about 1 each. Since the atomic size is 0.2 nm or more and the crystal grain size is 20 nm or less, the crystal grain boundary becomes discontinuous at the boundary surface between both layers. Therefore, the progress of corrosion along the grain boundaries is suppressed, and as a result, the reflectivity of the light-reflecting layer is favorably maintained without change over time, and the reproducing function is guaranteed with high reliability.

[Brief description of drawings]

FIG. 1 is an enlarged partial sectional view schematically showing a light reflecting layer according to an embodiment, and FIGS. 1 (a), (b), (c), and (d) show four types of laminated structures.

FIG. 2 is an enlarged partial sectional view of the optical disc.

FIG. 3 is an X-ray diffraction spectrum diagram of a light reflecting layer according to a first example and a fourth comparative example to the first example.

FIG. 4 is a diagram showing a structure of a light reflecting layer before and after an accelerated deterioration test for the first embodiment, in which FIG. 4 (a) shows a reflection optical microscope structure immediately before the start of the test and FIG. 4 (b) shows the structure after the test. The optical microscope organization of is shown.

FIG. 5 is a diagram showing a structure of a light reflecting layer before and after an accelerated deterioration test according to a first comparative example with respect to the first embodiment.
Shows the reflection optical microscope structure immediately before the start of the test, and FIG. 7B shows the optical microscope structure after the end of the test.

FIG. 6 is a diagram showing a structure of a light reflecting layer before and after an accelerated deterioration test according to a second comparative example with respect to the first example, and FIG.
Shows the reflection optical microscope structure immediately before the start of the test, and FIG. 7B shows the optical microscope structure after the end of the test.

FIG. 7 is a diagram showing a structure of a light reflecting layer before and after an accelerated deterioration test according to a third comparative example with respect to the first embodiment, and FIG.
Shows the reflection optical microscope structure immediately before the start of the test, and FIG. 7B shows the optical microscope structure after the end of the test.

FIG. 8 is a diagram showing the structure of a light reflecting layer before and after an accelerated deterioration test according to a fourth comparative example with respect to the first embodiment.
Shows the reflection optical microscope structure immediately before the start of the test, and FIG. 7B shows the optical microscope structure after the end of the test.

FIG. 9 is an X-ray diffraction spectrum diagram of a light reflecting layer according to a second example and a comparative example.

FIG. 10 is an X-ray diffraction spectrum diagram showing a part of the horizontal axis of FIG. 10 in an enlarged manner.

FIG. 11 is a diagram showing the structure of the light-reflecting layer before and after the accelerated deterioration test according to the second embodiment. FIG. 11 (a) shows the structure of a reflection optical microscope immediately before the start of the test, and FIG. The optical microscope organization of is shown.

FIG. 12 is a view showing a structure of a light reflecting layer before and after an accelerated deterioration test according to a comparative example with respect to the second example. FIG. 12 (a) shows a reflection optical microscope structure immediately before the start of the test, and FIG. The optical microscope structure after completion of the test is shown.

FIG. 13 is an X-ray diffraction spectrum diagram of a light reflecting layer according to a third example.

14A and 14B are diagrams showing a structure of a light reflecting layer before and after the accelerated deterioration test, in which FIG. 14A shows a reflection optical microscope structure immediately before the start of the test, and FIG. 14B shows an optical microscope structure after the test. Show.

FIG. 15 is an enlarged partial cross-sectional view showing a reproducing mechanism of the MO disc.

FIG. 16 is an enlarged partial sectional perspective view of an optical disc.

FIG. 17 is a schematic configuration diagram of a signal reproduction system in which an optical disc is arranged.

FIG. 18 is a transmission electron microscope image of polycrystalline aluminum.

FIG. 19 is an enlarged partial cross-sectional view of a conventional optical disc during signal reproduction.

[Explanation of symbols]

 1, 21 ... Optical disc 2 ... Substrate 3 ... Pit 4, 24 ... Light reflection layer 5 ... Protective layer 6 ... Semiconductor laser 7, 27 ... Laser light 9 ... Objective lens 10 ... Reflected light 11 ... Photodiode 12 ... Beam splitter 25 ... Magneto-optical recording layer 41 ... MO disc M1, M2 ... Thin film (first and second layers) M3 ... first phase M4 ... second phase M5 ... composition gradient film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Itabashi 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (17)

[Claims] 1. An optical element having a substrate and a light-reflecting layer provided on the substrate, wherein the light-reflecting layer is a laminated film composed of at least two types of layers having different compositions and / or structures. An optical element characterized in that the thickness of the at least two types of layers is 0.2 nm or more and 20 nm or less, respectively. 2. The laminated film comprises at least a first layer and a second layer, and the alternating lamination of at least the first layer and the second layer is repeated twice or more. 1. The optical element described in 1. 3. The optical element according to claim 2, wherein at least the first layer and the second layer each comprise an element, an alloy or a compound. 4. The optical element according to claim 2, wherein at least one of the first layer and the second layer is a layer containing 50 atom% or more of a metal. 5. The method according to claim 2, wherein at least the first layer and the second layer have an epitaxially grown structure, a polycrystalline structure, an amorphous structure or a mixed structure thereof.
Or the optical element described in 4. 6. The optical element according to claim 1, wherein light having a wavelength of 100 nm or more is used as incident light. 7. The optical element according to claim 2, wherein the composition of these layers is drastically changed at least at the interface between the first layer and the second layer. . 8. The method according to claim 2, wherein at least one of the first layer and the second layer has a structure in which the second phase is dispersed in the first phase. Optical element. 9. At least one of at least a first layer and a second layer is divided with a gap in the plane direction,
3. The layers on both sides are connected in this divided area.
The optical element according to any one of to 8. 10. An intermediate layer having a composition continuously changing from the composition of the first layer to the composition of the second layer is interposed between at least the first layer and the second layer, The abrupt composition change does not occur due to the interposition of the intermediate layer.
~ The optical element according to any one of 6, 8 and 9. 11. The optical element according to claim 2, wherein at least the first layer and the second layer have mutually different functions. 12. The optical element according to claim 2, wherein at least the first layer and the second layer are layers formed by a sputtering method, a vapor deposition method, a CVD method or a plating method. element. 13. The optical element according to claim 1, wherein the surface of the light reflecting layer opposite to the substrate is covered with a protective layer. 14. The substrate according to claim 1, wherein one or both of a substrate-side surface of the light reflection layer and a substrate-side surface of the light reflection layer are covered with a dielectric layer. Described optical element. 15. The method according to claim 1, further comprising a recording layer on which a predetermined signal is recorded or recordable, and the light reflecting layer is provided on the recording layer directly or via a dielectric layer. The optical element according to item 1. 16. An information recording medium, wherein at least a light-reflecting layer is formed on a substrate, and predetermined information is recorded in the information recording medium, wherein the light-reflecting layer is any one of claims 1 to 15. An information recording medium comprising the described light reflecting layer. 17. An information recording / reproducing apparatus configured to arrange the optical element according to claim 1 in an optical system and record / reproduce predetermined information.