JP2002170282A - Optical disk and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk where a characteristic such as a jitter and a modulation degree is improved and to provide its manufacturing method. SOLUTION: A reflection layer 4, a first protection film 5, a phase transition recording layer 6, a second protection layer 7 are successively formed on the surface of a baseboard 2 where grooves G and lands L are formed in advance in the optical disk 1. A smooth layer 3 with a 5 nm-30 nm thickness consisting of a dielectric body is inserted between the baseboard 2 and the reflection layer 4 in the optical disk 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk having high density and a method for manufacturing the same.

[0002]

2. Description of the Related Art Optical discs are DVD-RAM, DVD
-Widely used for RW and the like. In order to realize an optical disk having a high density of 7 to 8 GB or more and a recording / reproducing apparatus using the signal format used for DVD as it is, development of a semiconductor laser having an oscillation wavelength around 400 nm and a large NA (numerical aperture) Lenses having the following are being actively developed. On the other hand, in an optical disk, a reflection layer is formed on a transparent substrate for the purpose of a tilt margin (angle at which the disk surface deviates from the laser optical axis perpendicularly), and a phase change recording layer is formed on the reflection layer. ing.

FIG. 4 shows such a conventional optical disk.
This will be described with reference to FIG. FIG. 4 is a sectional view showing a conventional optical disc. In the conventional optical disk 9, grooves G and lands L are alternately formed in a disk radial direction on a transparent substrate 2 made of polycarbonate, polyolefin or the like, and a reflective layer 4, a first protective film 5, The phase change recording layer 6 and the second protective film 7 are sequentially laminated, and a transparent sheet-like substrate 8 is bonded to the surface of the second protective film 7 using an ultraviolet curable adhesive. Then, a laser beam is irradiated from the sheet-like substrate 8 side of the optical disk 9 to perform recording / reproducing light. Examples of the material of the sheet-like substrate 8 include polycarbonate and polyolefin.

Next, a method of manufacturing the optical disk 9 will be described. First, a Ni stamper on which a fine groove pattern is formed is manufactured by a mastering method of forming grooves or pits using a laser beam and an electroforming method of forming Ni. Further, a plastic material such as polycarbonate is melted and poured into the Ni stamper described above,
Injection molding is performed, and a mold of a stamper is transferred to this plastic material, thereby producing a transparent substrate 2 on which grooves G and lands L are formed. Thereafter, a reflective layer 4, a first protective film 5, a phase change recording layer 6, and a second protective film 7 are sequentially formed on the transparent substrate 2 by a sputtering method, and then the second protective film 7 is formed. An optical disk 9 is manufactured by laminating a sheet-like substrate 8 thereon using an ultraviolet curable adhesive.

[0005]

However, irregularities on the groove G and the land L of the transparent substrate 2 are roughened due to the surface condition of the stamper, the conditions of the injection molding, the material of the transparent substrate 2, and the like. The corresponding layers of the reflective layer 4 to the second protective film 7 are formed with corresponding irregularities, and the light scattered by the reflective layer 4 deteriorates characteristics such as noise and jitter during recording and reproduction. Had occurred. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical disk having improved characteristics such as jitter and modulation and a method of manufacturing the optical disk.

[0006]

Means for Solving the Problems A first invention of the present invention is:
In an optical disc in which a reflective layer, a first protective film, a phase change recording layer, and a second protective film are sequentially formed on a substrate surface on which grooves and lands are formed in advance, a dielectric material is interposed between the substrate and the reflective layer. An optical disk characterized in that a smooth layer having a thickness of 5 nm to 30 nm is inserted. Second
The invention is directed to a method of manufacturing an optical disc, wherein a reflective layer, a first protective film, a phase change recording layer, and a second protective film are sequentially formed on a substrate surface on which grooves and lands are formed in advance by sputtering. A method for producing an optical disk, characterized in that a high-frequency sputtering is performed on a substrate surface to form a smooth layer having a thickness of 5 nm to 30 nm before the formation of the optical disk.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk and a method of manufacturing the same according to the present invention will be described below with reference to the drawings.
The same components as those of the conventional example are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1 is an enlarged sectional view showing the optical disc of the present invention. FIG. 2 shows the cross-sectional shape of the transparent substrate in the optical disc of the present invention, which is shown by an atomic force microscope (Atomic Force).
It is a figure which shows the roughness of the groove | channel and land measured by Microscope (AFM for short). FIG.
FIG. 3 is a view showing the roughness of the surface of a groove and a land measured by an atomic force microscope on the cross-sectional shape of a transparent substrate on which a smooth layer is formed in the optical disc of the present invention. 2 and 3, the vertical axis represents the height (Å) to the land surface when measured with the lowest bottom of the groove as a reference, and the horizontal axis represents the length (μm) in the track direction.

As shown in FIG. 1, the optical disk 1 of the present invention
In the conventional optical disc 9, a smooth layer 3 having a predetermined thickness is inserted between the transparent substrate 2 on which the grooves G and the lands L are formed and the reflective layer 4; It is. The material of the smoothing layer 3 is Zn
S-SiO ₂ (SiO ₂ : 20 mol), ZnS, SiO
₂ , inorganic thin films such as silicon nitride and aluminum oxide, S
a metal such as i, Ge, Al, Ti, Zr, Ta or the like; a nitride of a semiconductor; a metal such as Ti, Zr, Hf, Si or a semiconductor carbide; a metal such as ZnS, In ₂ S ₃ , TaS ₄ , GeS ₂ or Semiconductor sulfides and mixtures of two or more of these compounds are preferred because of their high heat resistance and chemical stability.

Here, as a result of examining the thickness of the smooth layer 3, it was found that the following range was optimal. Smooth layer 3
When the thickness was 5 nm or less, stable recording and reproduction could not be performed. This is because the groove G and the land L of the transparent substrate 2 are
The irregularities on the upper surface cannot be absorbed by the smoothing layer 3, and irregularities are formed on the surface of the reflective layer 4. When the thickness of the smoothing layer 3 was 30 nm or more, the recording sensitivity characteristics deteriorated. This is presumably because, when the dielectric layer is formed, the width and depth of the groove G are deformed and the recording sensitivity is lowered, so that reading by the laser beam is not stable. On the other hand, the thickness is 5 nm
In the range of ３０30 nm, good recording and reproduction can be performed.
Good recording sensitivity characteristics were obtained. Therefore, it was found that the optimum thickness of the smoothing layer 3 was in the range of 5 nm to 30 nm.

Next, the recording and reproducing characteristics of the optical disk 1 of the present invention and the conventional optical disk 9 were compared. In this evaluation, a linear velocity of 4.6 was applied to the groove G from the sheet-like substrate 8 side.
After recording at 8/16 modulation random pattern at m / s, the slice is sliced at the center of the amplitude of the reproduction signal from the optical disk 1 and the clock to d of the reproduction signal
The measurement was carried out by measuring atajitter. The wavelength of the laser light is 405 nm, and the clock cycle is 19.1 ns. For the groove detection, a time interval analyzer (TA320, manufactured by Yokogawa Electric Corporation) was used. The recording conditions are a peak power of 8.0 mW, an erasing power of 4.0 mW, and a cooling power of 0.5 mW.

As a result, the conventional optical disk 9 has a jitter value of 11.5% and a modulation factor of 49.6%, while the optical disk 1 of the present invention has a jitter value of 7.4% and
The modulation factor was 50.3%, and the jitter value and the modulation factor were improved. As described above, according to the embodiment of the present invention, the thickness of the conventional optical disc 9 is 5 nm to 30 n between the transparent substrate 2 on which the groove G and the land L are formed and the reflective layer 4.
m smooth layer 3 is inserted.
Thus, the unevenness on the groove G and the land L can be absorbed, so that the reflective layer 4 to the second protective film 7 formed thereon have reduced unevenness corresponding to the unevenness, and have good recording sensitivity characteristics. In addition, the optical disc 1 having stable recording and reproduction can be obtained. In addition, the jitter value and the degree of modulation can be greatly improved as compared with the related art.

Next, a method for manufacturing the optical disk 1 of the present invention will be described. (Transparent Substrate Preparation Step) First, using a Ni stamper provided with a groove having a depth of 35 nm and a track pitch of 0.75 μm, a transparent substrate 2 injection-molded in the same manner as in the conventional example is prepared. At this time, the thickness of the transparent substrate 2 is 1.2 mm.

(Smooth Layer Forming Step) An Al alloy target, a ZnS—SiO ₂ target and AgInSbTe (Ag: In: Sb: Te =
5: 5: 60: 30) High frequency (RF) alloy target
And into a sputtering device that is also used for direct current (DC). After evacuating the inside of the sputtering apparatus to 6 × 10 ⁻⁵ Pa,
After introducing 1.6 × 10 ⁻¹ Pa of Ar gas and setting the output of the high frequency power supply to 400 W, the ZnS—SiO ₂ target was subjected to high frequency sputtering (RF sputtering) while rotating the transparent substrate 2 at 60 revolutions per minute. ) To form a smooth layer 3 having a thickness of 5 nm to 30 nm at a sputtering rate of 0.2 nm / s. The smooth layer 3 absorbs irregularities formed on the grooves G and the lands L on the transparent substrate 2, and can form a flat surface on this surface. Therefore, this unevenness does not occur in each layer formed on the smooth layer 3.

(Reflection Layer Forming Step) Subsequently, in the same manner as described above, an Al alloy target is sputtered to form a reflection layer 4 having a thickness of 110 nm on the smooth layer 3. As described above, since the surface of the smooth layer 3 is flat, the reflective layer 4 formed thereon has a flat surface without irregularities.

(First Protective Film Forming Step) Further, similarly to the above, a ZnS-SiO ₂ target is sputtered,
A first protection film 5 having a thickness of 15 nm is formed on the reflection layer 4.

(Recording layer forming step) Next, AgInSbTe (Ag: In: Sb: Te = 5:
5:60:30) A phase change recording layer 6 having a thickness of 20 nm is formed on the first protective film 5 by sputtering an alloy target.

(Second Protective Film Forming Step) After that, a ZnS-SiO ₂ target is sputtered in the same manner as described above.
A second protective film 7 having a thickness of 50 nm is formed on the phase change recording layer 6.

(Laminating Step) Next, after the transparent substrate 2 on which the layers from the smooth layer 3 to the second protective film 7 are formed is taken out of the sputtering apparatus, the surface of the second protective film 7 has a thickness of 0.1 mm.
An optical disk 1 shown in FIG. 1 is obtained by laminating a 1 mm polycarbonate sheet-like substrate 8 using an ultraviolet curable adhesive. At this time, the UV curable adhesive is 405 nm.
A material having low light absorption is used in the vicinity.

Here, the surface roughness of the transparent substrate 2 injection-molded in the (transparent substrate preparing step) and the surface roughness of the smooth layer 3 after the completion of the (smooth layer forming step) are examined using an atomic force microscope. The effect of the smooth layer 3 which is a feature of the present invention was examined. The results are shown in FIGS. 2 and 3
As shown in (1), the roughness of the surface of the transparent substrate 2 injection-molded in the (transparent substrate preparation step) was 7 nm, and the roughness of the surface of the smooth layer 3 after the completion of the (smooth layer formation step) was 3 nm. .
As described above, if the smooth layer 3 is formed on the transparent substrate 2, the surface of the smooth layer 3 can be made substantially flat. It also shows that the layer formed thereon can be made flat.

As described above, according to the method for manufacturing the optical disk 1 of the present invention, the high-frequency sputtering is performed before the formation of the reflective layer 4.
Since the smooth layer 3 having a thickness of 5 nm to 30 nm is formed on the transparent substrate 2 on which the grooves G and the lands L are formed in advance, the surface of the smooth layer 3 absorbs the unevenness of the grooves G and the lands L on the transparent substrate 2. A flat surface can be formed. Therefore, at the time of recording / reproduction, irregular reflection generated in the reflection layer 4 formed on the smooth layer 3 is reduced, and characteristics such as jitter and modulation can be improved.

In order to make the optical disk 1 usable for recording, the following initialization is performed. This initialization is performed using an initialization device and an evaluator disclosed in Japanese Patent Application Laid-Open No. 7-282475. After the optical disc 1 is mounted on the spindle of this initialization device,
While rotating at a linear velocity of 3 m / s, a laser beam having a wavelength of 830 nm is moved in the radial direction from the inner circumference to the outer circumference at a power of 300 mW to irradiate the phase change recording layer 6 and overheat to obtain a high reflectance. Initialize by changing to the state. The evaluator is used to measure the reflectance. At this time, the laser beam diameter is preferably larger than the track width so that a plurality of tracks can be irradiated, and preferably longer in the radial direction. Specifically, the shape of the laser beam diameter is 2 μm in the track direction.
m, 20 μm in the radial direction.

[0022]

According to the optical disk of the present invention, there is provided an optical disk in which a reflective layer, a first protective film, a phase change recording layer, and a second protective film are sequentially formed on a substrate surface on which grooves and lands are formed in advance. Since a smooth layer made of a dielectric material having a thickness of 5 nm to 30 nm is inserted between the substrate and the reflective layer, the unevenness on the groove or land can be absorbed by the smooth layer. In each layer of the reflective layer or the second protective film, the corresponding unevenness is reduced,
An optical disc having good recording sensitivity characteristics and capable of stable recording and reproduction can be obtained. In addition, the jitter value and the degree of modulation can be greatly improved as compared with the related art. According to the optical disk manufacturing method of the present invention, the sputtering method
In a method for manufacturing an optical disk in which a reflective layer, a first protective film, a phase change recording layer, and a second protective film are sequentially formed on a substrate surface on which grooves and lands are formed in advance, high-frequency sputtering is performed before forming the reflective layer. And a thickness of 5 nm to 3
Since a smooth layer having a thickness of 0 nm is formed, the smooth layer can form a flat surface absorbing the unevenness of the grooves and lands on the transparent substrate. For this reason, at the time of recording / reproduction, irregular reflection generated in the reflective layer formed on the smooth layer is reduced, and characteristics such as jitter and modulation can be improved.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an optical disk of the present invention.

FIG. 2 is a diagram showing roughness of a groove and a land surface obtained by measuring a cross-sectional shape of a transparent substrate in an optical disc of the present invention with an atomic force microscope.

FIG. 3 is a diagram showing the roughness of grooves and lands measured by an atomic force microscope on a cross-sectional shape of a transparent substrate on which a smooth layer is formed in the optical disc of the present invention.

FIG. 4 is a cross-sectional view showing a conventional optical disc.

[Explanation of symbols]

1 ... optical disk, 2 ... transparent substrate (substrate), 3 ... smooth layer,
4 reflective layer, 5 first protective film, 6 phase change recording layer, 7
Second protective film, 8: sheet substrate, G: groove, L: land

Claims (2)

[Claims] 1. An optical disk having a reflective layer, a first protective film, a phase-change recording layer, and a second protective film sequentially formed on a substrate surface on which grooves and lands are formed in advance, wherein the substrate, the reflective layer, 5n thickness of dielectric material between
An optical disc having a smooth layer of m to 30 nm inserted therein. 2. A method for manufacturing an optical disk, wherein a reflective layer, a first protective film, a phase change recording layer, and a second protective film are sequentially formed on a substrate surface on which grooves and lands are formed in advance by sputtering. A method for manufacturing an optical disc, comprising forming a smooth layer having a thickness of 5 nm to 30 nm on a substrate surface by high frequency sputtering before forming a layer.