JP3146766B2 - Optical disc and optical disc reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk and a method for reproducing an optical disk, and more particularly to a technique for recording and reproducing high-density information.

[0002]

2. Description of the Related Art An optical disk capable of storing high-density data and capable of processing information at high speed has attracted attention as an external memory of a computer. In particular, with a size of 5.25 inches in diameter, a write-once type in which information can be written only once and a magneto-optical type in which information can be rewritten,
In the case of a 3.5-inch diameter, a magneto-optical type and a read-only ROM type and a partial ROM type in which magneto-optical and ROM are mixed are standardized by the ISO standard, and will be widely spread in the market in the future. Is expected.

[0003] Recently, optical discs have begun to be applied in the digital audio field. For example,
A player using a write-once type optical disk or a magneto-optical disk as a master source in digital multi-track recording of 24 to 48 tracks is sold. In addition to products for professionals, CD-Rs (write-once compact discs) and MDs (minidiscs) have emerged as products for general consumers, and future trends are attracting attention. On these optical discs, a guide for orderly arranging information marks by a laser beam from an optical pickup of a recording / reproducing apparatus, that is, a guide for tracking is formed in a concave or convex groove from the inner periphery to the outer periphery of the disc. It is formed in a spiral shape. This groove is called a guide groove.

[0004] To further explain the guide groove in detail, as defined in the ISO standard, a part that is concave when viewed from the optical pickup, that is, a part that is far away is called a land, and is viewed from the pickup. The portion that becomes convex when it is closed, that is, the portion that becomes close, is called a groove. Information is written to either lands or grooves. When data is written to a land, it is called a land recording method, and when data is written to a groove, it is called a groove recording method. The distance from the center of a land (groove) to the center of an adjacent land (groove) is called a track pitch.

[0005] In recent years, in order to accumulate information at a higher density, a technique of including information in a guide groove which has only served as a guide for tracking has begun to be used. This is a groove or land,
This is due to the method of meandering left and right. That is, the groove or the land is meandered right and left according to the information to be recorded. At this time, the meandering carrier frequency is
If a frequency outside the tracking band is selected, there is no worry that tracking will be disturbed by the meandering of the grooves or lands (tracking will follow the meandering groove by moving left and right). Tracking is performed as if there were not. Therefore, when tracking a groove or land, the amount of reflected light fluctuates in accordance with the meandering component, and this reflected light is received by a photo sensor, and a change in the amount of light is converted into a change in current. Meandering information can be reproduced. One example of such an optical disk is shown in FIGS.

The above-mentioned CD-R (write-once type compact disc) and MD (mini-disc) also use the technique of meandering grooves. In this case, the meandering carrier frequency is 22.05 KHz and the meandering amplitude is 30 nm. By the way, the shapes of the grooves of optical discs currently on the market are U-shaped and V-shaped.
There are types. In the case of a U-shape, assuming that the width at the _top of the groove is W _top and the width at the bottom of the groove is W _bottom , the groove width W is W = (W _top + W _bottom ) /
2 and V = W _top in the case of a V-shape. The height from the bottom of the groove to the top of the land is called the groove depth or the height of the land.

Here, the actual dimensions of the guide groove are as follows. In the land recording type, the groove width is 0.4 μm to 0.8 μm, and the groove depth is λ where the wavelength of the recording / reproducing laser is λ. If the refractive index of the substrate is n,
λ / (7 · n) to λ / (8 · n). Also,
Groove width of 0.8 μm to 1.2
μm, and the groove depth is λ / (7 if the wavelength of the recording / reproducing laser beam is λ and the refractive index of the substrate is n.
· N) to λ / (8 · n).

The track pitch is 1.6 μm in any of the above recording systems. Recently, a proposal has been made to make the track pitch smaller in order to record higher-density information.

[0009]

As described above, it has been proposed to reduce the track pitch as a means for further increasing the density of a conventional optical disk. However, in a conventional pickup equipped with a semiconductor laser having a wavelength of 780 to 830 nm and an objective lens having a numerical aperture (NA) of 0.5 to 0.55, when the track pitch is smaller than 1.4 μm, data is written on adjacent grooves or lands. Problems such as an extremely large influence of information (called crosstalk) and an extremely small tracking error signal required for tracking have occurred. To solve this problem, semiconductor lasers having a wavelength of 670 to 690 nm have been developed, but are still in a technically unsatisfactory condition such as the beam shape and output of the laser light.

Therefore, as a means for realizing higher density, a technique of meandering the above-mentioned groove or land at a high carrier frequency has been attracting attention. However,
In this method, if the meandering carrier frequency is too high, there is a problem that the meandering information becomes difficult to read. To avoid this, attempts have been made to increase the meandering amplitude. However, since noise during reproduction is increased, there has been a problem that information written on lands or grooves is particularly difficult to read. Was.

[0011]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, in an optical disk having a groove meandering according to information, the width of the groove is at least half the track pitch. The ones that have more information, also in the form of land height changes,
It has been found that the effects of crosstalk can be suppressed to a level that does not cause any practical problems, and that high-density data can be accumulated.

An optical disk having lands meandering in accordance with information has a width wider than at least one half of a track pitch and has information in the form of a change in groove depth. Have also been found to achieve the objects of the present invention. Further, the inventor
To find a method of reproducing information, such as reading information by meandering the groove while tracking the groove, and at the same time or at another time, reading information by changing the height of the land while tracking the land Reached.

The present invention, on the contrary, reads the information due to the meandering of the land while tracking the land, and simultaneously or at another time, changes the depth of the groove while tracking the groove. It also includes a method of reproducing information, such as reading information by the above method.

[0014]

The optical disk according to the present invention not only increases the density by meandering the groove, but also records information by changing the height of the land, which was conventionally constant, to achieve a further higher density. Things. That is, the feature of the present invention is that information is also included in a land that does not include information in the conventional groove meandering technique.

In the present invention, one point is how to give information to the land. The present inventor has proposed a method of changing the height of the land in accordance with the information to be recorded. I found the most suitable. Furthermore,
It has been found that in order to easily manufacture such an optical disc, it is better to change the height of the land into a wave shape.

The change in the height of the land means that the land meanders not vertically but horizontally. If the land of such an optical disk is tracked by an optical pickup, the amount of light reflected from the optical disk changes according to the fluctuation component of the height of the land. If converted into a change, information based on a change in the height of the land can be reproduced. One example of such an optical disk according to the present invention is shown in FIGS.

Since not only the groove meandering information but also the land height change information is used, naturally, the land height change information leaks into the groove meandering information, or conversely, the groove height change information. It is expected that the phenomenon in which the meandering information leaks into the land height change information, that is, crosstalk, will be particularly problematic. To solve this problem, it has been found that crosstalk can be suppressed by making the groove width wider than half the track pitch.
The reason is that when the groove width is wider than one half of the track pitch, the fluctuation in the amount of reflected light due to the change in the land width becomes smaller when tracking the land, that is, the fluctuation in the amount of reflected light due to the meandering of the groove. The effects of the components are relatively small. Therefore, when the land is tracked, almost only the fluctuation component of the reflected light amount due to the change in the height of the land is captured. For exactly the same reason, when tracking the groove, the influence of the fluctuation component of the reflected light amount due to the fluctuation of the land height is relatively small. Therefore, when tracking the groove, almost only the fluctuation component of the amount of reflected light due to the meandering of the groove is captured.

In this manner, the density can be at least twice as high as that of the conventional optical disk without reducing the track pitch and without making the groove meander at a high carrier frequency. In the above, the case where the height of the land is changed by meandering the groove has been described. However, it is needless to say that the depth of the groove may be changed by meandering the land.

[0019]

An embodiment of the present invention will be described with reference to FIG. (1) A copper master having a precise plane and a diameter of 350 mm was prepared (FIG. 7 (a). (2) After spin-coating the master surface with hexamethyldisilazane as a primer, AZ1350 photoresist (manufactured by Hoechst) was applied. The layers were spin-coated and pre-baked at 100 ° C. for 30 minutes (FIG. 7 (b)).

(3) Using a laser cutting machine equipped with an argon laser having a wavelength of 457.9 nm, a portion corresponding to the groove was exposed in a region from a radius of 72 mm to 148 mm while meandering. At this time, the track pitch was 1.6 μm, the linear velocity was 10 m / s, and the meandering information was a carrier frequency of 1 MHz.
The random data of z, meandering amplitude was 40 nm. (4) After spin development with an inorganic alkali developer, post-baking was performed in a clean oven at 120 ° C. for 30 minutes (FIG. 7).
(c)).

(5) The master is placed in a dry etching apparatus (DEA506T manufactured by Nidec Anelva), and the degree of vacuum is 1.0 × 10 ⁻⁴ Pa.
After evacuation, sputter etching was performed by introducing an argon gas. The etching conditions at this time were an argon gas flow rate of 10 SCCM, a gas pressure of 0.5 Pa, an RF power of 500 W, a self-bias voltage of -500 V, and an etching time of 20 minutes.

(6) The remaining resist was removed by performing ashing by replacing the argon gas with oxygen. In this way, a meandering groove was formed on the surface of the copper master (FIG. 7D). The groove width at this time is 1.1 μm
And the height of the land was 100 nm. (7) Using a mechanical cutting machine, the surface was cut while tracking along the land on the surface of the copper master (Fig. 7 (e)). Tracking was controlled by monitoring a change in the stylus pressure of a stylus provided in front of the cutting blade. At this time, the linear velocity was 1 m / s, and the cutting blade was moved up and down in accordance with random data having a carrier frequency of 50 KHz to cut the land so that the height of the land changed in a wave shape. The height of the land after cutting was a minimum of 80 nm and a maximum of 100 nm.

(8) After nickel electroforming was performed on the copper master, a stainless steel backing plate was adhered to the electroformed back surface with an epoxy adhesive (FIG. 7 (f)). (9) The copper master and the nickel electroformed layer were peeled off to obtain a stamper. (FIG. 7 (g)) Using this stamper, a disk substrate is manufactured by transferring a pattern of meandering grooves and lands having changed heights on the surface of a glass substrate by a 2P (ultraviolet curing resin) molding method. Then, an SiN layer, a TbFeCo layer, and a SiN layer were sequentially formed on this substrate by sputtering, and then a protective glass substrate was bonded to the film surface with an ultraviolet curable adhesive to obtain an optical disk.

The optical disk manufactured as described above was subjected to a wavelength of 830 nm, a numerical aperture of 0.55, a vignetting coefficient of 1.0, and a wavefront aberration of 0.03.
0 λ (rms value), the polarization state of the laser is linearly polarized light,
The data was reproduced by a recording / reproducing apparatus equipped with an optical pickup in the direction parallel to the guide groove. The linear velocity at this time is 10 m / s, and the laser beam intensity during reproduction is 1.
0 mW.

The evaluation was performed as follows. First, a reflected light amount signal when tracking a groove was input to a data error rate measuring circuit, and the bit error rate of random data having a carrier frequency of 1 MHz, which was the meandering information of the groove, was measured. Table 1 shows the results. Next, the reflected light amount signal when the land was tracked was input to a data error rate measurement circuit, and the bit error rate of random data having a carrier frequency of 500 KHz, which is land height change information, was measured.
Table 2 shows the results. From these results, it can be seen that both the groove meandering information and the land height change information can be reproduced with a practically sufficiently low error rate.

The master for producing the stamper may be made of a metal or alloy such as gold, silver, aluminum, stainless steel, iron or nickel, or ceramic such as glass or quartz, in addition to copper. Further, a configuration in which an aluminum plate is coated with a copper thin film may be used.

[0027]

As described above, according to the present invention, a high-density optical disk having a sufficient reliability and a reproducing method thereof are provided.

[0028]

[Table 1]

[0029]

[Table 2]

[Brief description of the drawings]

FIG. 1 is an enlarged top view showing a meandering groove and a land with a changed height of an optical disc in an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA ′ of FIG.

FIG. 3 is a sectional view taken along line BB ′ of FIG. 1;

FIG. 4 is an enlarged top view showing a meandering groove of a conventional optical disc.

FIG. 5 is a sectional view taken along the line CC ′ of FIG. 4;

FIG. 6 is a sectional view taken along line DD ′ of FIG. 4;

FIG. 7 is a manufacturing process diagram of a stamper used for manufacturing an optical disc in the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... meandering groove 2 ... Land 3 ... High part of land 4 ... Low part of land 5 ... Copper master 6 ... Photoresist 7 ... Nickel electroformed layer 8 ... epoxy adhesive 9 ... stainless steel backing plate

Claims (7)

(57) [Claims] 1. An optical disk having a meandering groove, wherein the width of the groove is wider than at least half the track pitch, and the height of a land is changed. 2. The optical disk according to claim 1, wherein the height of the land changes in a wave shape. 3. An optical disk having meandering lands, wherein the lands have lands that are at least wider than at least half the track pitch, and the depths of the grooves are changed. 4. The optical disk according to claim 3, wherein the depth of the groove changes in a wave shape. 5. An optical disk having a meandering groove, wherein the height of a land changes. 6. A method for reproducing information, comprising: reading information due to the meandering of the groove by tracking the groove; and reading information by changing the height of the land by tracking the land. 7. By tracking lands,
A method for reproducing information, comprising reading information due to the meandering of the land and tracking the groove, thereby reading information according to a change in the depth of the groove.