JPH0766573B2 - optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an optical disc which has good signal characteristics and can be obtained with a high yield.

[Conventional technology]

In a writable optical disc, information is recorded by writing information pits on a track with an optical head, that is, a light beam, while information is reproduced by reading the information pits with a light beam. At this time, a continuous guide groove is provided to make the optical head follow a predetermined track. As a method of recording information, a method of recording information between the grooves (land recording method) is generally adopted. In the land recording method, the guide groove is usually provided continuously with respect to the track, or as shown in FIG.
Is formed in advance after the header information portion 3 (4 is a sector mark information portion), and a 1-byte mirror mark 5 having no guide groove is provided, and the guide groove 1 is continuously provided for other portions except this portion. ing.

The header information includes information such as a sector mark, a synchronization mark, a track address, a sector address, and a CRC signal, and these information pits are formed together with the guide groove when the optical disc is manufactured.

Therefore, in manufacturing a metal master (stamper), two laser beams are used on a glass master coated with a photoresist, that is, one laser beam is used for header information and the other laser beam is used for guiding grooves. The method of exposing and recording is usually used. After exposure, apply a metal plating such as Ni on the master obtained by development, peel it off from the master of the plated part to create a metal master, duplicate the optical disk substrate from this, and then write information pits on the substrate An optical disc is manufactured by providing a recording layer. The reproduction signal of the header portion of this optical disc has a standard value, for example, VFO (Variable Frequency).
Oscillator) signal modulation degree (I vfo / I o) ≧ 0.25, sector mark signal modulation degree (I sm / I o) ≧ 0.5, and the standard values are determined in various evaluation items.

[Problems to be solved by the invention]

However, it is difficult to obtain an optical disk satisfying all the various signal standard values and having a good signal waveform with a high yield.

That is, the shape of the guide groove and the information pit in the header portion of the optical disk has a great influence on the signal characteristics thereof.

At the time of recording on the master, the laser beam modulated by the header information signal and the laser beam modulated for the groove are simultaneously exposed and recorded in the header information portion.
The intensity distribution on a plane perpendicular to the optical axis of the laser beam has a Gaussian distribution, and in this distribution, grooves and pits are formed at the portions having the intensity exceeding the photosensitivity threshold of the photoresist. On the other hand, the portion between the information pit and the groove in the header portion has an irradiation power lower than the exposure threshold, but is exposed twice by the groove recording laser beam and the information pit recording laser beam. A slight film loss occurs. Further, the two laser beams affect each other, and the optimum conditions cannot be obtained independently. The inventors of the present invention have found that such a tendency is remarkable especially in the sector mark portion where the long hole pit is recorded.

In addition, if the irradiation power of the laser for recording information pits is reduced during recording of the master disc in order to suppress such an influence, it is difficult to obtain sufficient signal strength in the VFO section, which is a continuous section of short hole pits, etc. is there.

On the other hand, even when the optical disk resin substrate is reproduced from the metal master by injection molding, it is necessary to fill the resin in a narrow hill portion between the information pit portion and the groove portion of the header portion with a high transfer rate, and Selection is not always easy.

Due to the above effects, the depth of the groove and the information pit is effectively reduced, and the hill portion between the groove and the information pit is narrowed, so that sufficient signal strength cannot be obtained, and the sector mark portion is Inversion of the signal waveform as shown in FIG. 2 occurs, which causes a problem during reading.

In order to solve this problem, it is important to optimize the laser exposure conditions, photoresist absorption conditions, and development conditions during master recording, and to optimize various molding parameters when manufacturing disk substrates from the metal master. However, the range of optimization conditions is narrow, and it is difficult to obtain a good disc with high yield and good reproducibility.

It is an object of the present invention to provide an optical disc having a guide groove in which the appropriate operating range of the above manufacturing conditions, particularly the laser recording condition is enlarged, and an optical disc having good signal characteristics can be obtained with a high yield. is there.

[Means for solving problems]

The present invention, in an optical disc having a guide groove for tracking a light beam for writing or reading information on the optical disc, does not provide a guide groove in part or all of the portion in which header information is recorded in advance. The present invention provides an optical disc characterized in that the portion thereof is a mirror surface.

In the optical disc of the present invention, it is necessary not to provide the guide groove in a part or the whole of the portion where the header information is recorded, but it is preferable that the guide groove is not provided only in a part, particularly in the sector mark portion. preferable.

In the optical disc of the present invention, even if the guide groove is not provided in the portion where the header information is recorded, the tracking characteristics are hardly deteriorated, the influence of the groove recording laser beam is eliminated, and the amplitude of the reproduction signal of the sector mark portion is increased. Take
In addition, the irradiation condition range of the information pit recording laser that can eliminate the inversion of the sector mark reproduction signal can be made large, and the elongated hill portion between the groove and the pit is eliminated, so that this It is possible to obtain the effect that the resin can be easily filled in the portion.

The present invention will be described in detail below with reference to the drawings. Third
The figure shows a guide groove and a sector mark signal pit which are an example of the optical disc of the present invention. The guide groove is not provided in the sector mark signal pit portion and the surface is a mirror surface.

Recording of header information and guide grooves on the master is performed using a two-beam type laser cutting device as shown in the schematic view of FIG. That is, the glass master 6 coated with photoresist to a predetermined thickness is rotated by the spindle motor 7 at a predetermined speed. On the other hand, a laser beam 10 for recording information pits passes through an optical modulator 11, and a laser beam 8 for groove recording passes through an optical modulator 9
The waveform signal is modulated according to the information shown in the figure. The upper waveform is for forming the header information pit, and the lower waveform is for forming the guide groove. The upper part of both waveforms shows the laser beam turned on, while the lower part shows the laser beam turned off. Therefore, in FIG. 5, since the guide groove is not provided in the portion where the information pit of the sector mark is formed, the laser beam is turned off. The modulated laser beams pass through a lens system (not shown) for beam adjustment, and the beam modulated for groove recording is reflected by a mirror 12 and a beam splitter.
After passing through 13, after being reflected by the mirror 14 together with the information pit recording laser beam whose optical axis is aligned at a predetermined interval,
Through the objective lens 15, the glass master 6 coated with the photoresist in a predetermined thickness is irradiated. After exposure, development is performed to obtain a master having header information pits and guide grooves. Generally, the track pitch of the master is about 1.6 μm, the width of the guide groove is 0.4 to 0.5 μm, and the information pit width is generally 0.5 to 0.6 μm.
m is formed. Then, a metal master (stamper) is produced from this master by a known method. For example, the glass master disk with the header information recorded is subjected to a conductive treatment by Ni sputtering and then electroplated with Ni.After the plating is completed, the plating is peeled off from the glass master disk, the inner and outer perimeters of the plated plate are cut, and the backing is performed. Metal master (stamper) by polishing, washing and drying
Can be produced.

This metal master is placed in a mold of an injection molding machine, and a resin for an optical disk substrate (for example, polymethylmethacrylate, polycarbonate, etc.) is injection molded to manufacture an optical disk resin substrate. Then, a known recording medium, for example, a low melting point metal such as tellurium or cerium, an organic recording medium or the like is provided on the substrate by vapor deposition, sputtering or the like to form a recording layer, whereby an optical disk is produced. Further, these recording layers may be provided not only for write-once (WRITE-ONCE) recording media, but also for recording and erasing (ERASABLE) disk recording media such as magneto-optical and phase change type recording media.

The present invention can be applied to both the concentric circular groove method and the spiral groove method.

〔Example〕

FIGS. 6, 7 and 8 are diagrams showing a reproduced waveform of a part of the header information of the 130 mmφ optical disc of the present invention. No. 6 is a standard condition at a radius of 40.5 mm using a laser cutting device using an argon laser.
Information recording beam output 111 at 2.5 mm against standard conditions
% And groove recording beam output 113%, the exposure condition is 44.
The optical disc obtained by the above method was applied to the evaluation device from the master obtained by exposing and recording on the photoresist layer with beam outputs of 121% and 127% respectively at 5 mm, and the obtained header information section Although the reproduced waveforms are shown, the reproduced waveforms are all good. Also, the respective sector mark signal modulation degrees are 0.66, 0.71 and 0.77, which satisfy the standard values.

On the other hand, FIGS. 9, 10 and 11 show reproduction waveforms of an optical disc obtained by exposing and recording with the above beam output by the conventional recording method, respectively. Inversion occurs in the playback waveform of. The degree of modulation of the sector mark signal is also
0.62, 0.54, 0.45 and good under optimal exposure conditions,
Even a slight change in output will greatly decrease and will not satisfy the standard value. This indicates that the allowable range of exposure conditions is very narrow.

〔The invention's effect〕

The optical disc of the present invention has a good operating range of manufacturing conditions, particularly a range of laser irradiation conditions for writing, and good signal characteristics without impairing the reproduction performance of header information recorded in advance on the optical disc. It can be obtained with a high yield.

[Brief description of drawings]

FIG. 1 is a schematic view showing an arrangement of pits and grooves in a header portion of a conventional optical disk having guide grooves. FIG. 2 shows an example of a reproduced signal waveform of a header portion of an optical disc having a conventional guide groove. FIG. 3 is a schematic view showing the arrangement of pits and grooves in the header portion of the optical disc of the present invention. FIG. 4 is a schematic block diagram of a two-beam type laser cutting device. FIG. 5 shows the waveform of the laser light written on the master. 6 to 8 show signal reproduction waveforms of the header portion of the optical disc of the present invention, and FIGS. 9 to 11 show signal reproduction waveforms of the header portion of the conventional optical disc. 1 ... Guide groove, 2 ... Information pit, 3 ... Header information part, 4 ... Sector mark part, 5 ... Mirror mark

Claims (1)

[Claims] 1. An optical disc having a guide groove for tracking a light beam for writing or reading information on or from the optical disc, wherein the guide groove is provided in a part or all of a portion in which header information is recorded in advance. Without
An optical disc characterized in that the portion is a mirror surface.