JPH10124936A - Disk pit shape control method and disk recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optimal pit shape by controlling the on/off timing of a modulated digital signal to be recorded. SOLUTION: Digital data to be recorded is modulated for adding an error correction code by a digital signal converter 6 and then a digital signal is controlled by a duty factor controller (DC) 8. A signal outputted from the DC 8 is used to actuate an optical modulator 3 by an optical modulator driving circuit 7 according to the controlled digital signal and a laser beam is turned on/off. The DC 8 is composed of an H side pulse reducing circuit and an H side pulse expanding circuit, the reducing circuit being for reducing a signal level H side pulse and the expanding circuit being for expanding the same to an optional pulse width by a select switch. Thus, a basic digital signal, in this case an EFM modulated digital signal, is freely controlled within a select range by the DC 8. Thus, the number of control parameters is increased for stamper manufacturing in a disk manufacturing process and optimal pit formation of a disk is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pit shape control method for a disk on which a digital signal is recorded by pits, and a disk recording apparatus.

[0002]

2. Description of the Related Art The process of manufacturing a disk can be divided into two processes, a mastering process of creating a stamper and a replication process of copying a large number of disks from the stamper. The mastering step is a step of exposing the surface of the glass master to which the photoresist has been applied with laser light, and developing a stamper through the steps of development, conductive film treatment, and electroforming.

FIG. 6 shows a general configuration of a conventional case of exposing with a laser beam. Light emitted from a laser oscillator 11 passes through an optical lens 12 and is turned on and off by an optical modulator 13. The light passes through several optical elements, passes through an objective lens 14, and is coated with a photoresist on a glass master 1.
5 to expose the photoresist. On the other hand, the digital data to be recorded is modulated by the digital modulator 16 such as adding an error correction code, and then the optical modulator 13 is turned on and off through an optical modulator driving circuit 17. The optical modulator 13 turns on and off the laser light according to the modulated signal. By developing the master 15 on which the signal is recorded in this manner, pits corresponding to the modulated digital signal are formed on the surface of the master. A stamper, which is a mold for molding a disk from the master 15 by an appropriate method such as electroforming, is manufactured, and a large number of disks are manufactured from the stamper by an appropriate method such as injection molding.

[0004]

The pits formed on the master are accurately formed with a certain error from the modulated digital signal. This is because the shape (particularly the length) of the pit changes depending on the power of the laser beam, the development time of the master, the photosensitive performance of the photoresist, and the like. If these factors are completely controlled, FIG. As shown in ()), pits completely corresponding to the digital signal are formed. However, such complete control is impossible in practice, and a pit shorter by p as shown in FIG. 8A or a pit longer by q as shown in FIG. 8C is formed. Or The “shift” such as p and q is called asymmetry. Asymmetry is largely independent of the length of the recorded pits, and occurs approximately equally in pits of any length. In FIG. 8, T3 and T5 indicate the length of a pit or a region where no pit is formed.

[0005] In the pit shape, FIG.
As shown in (b), the edge, that is, the edge of the pit is not vertical but is inclined, and thus the general shape of the pit is shaped like a soccer stadium. The asymmetry and the angle of the edge change depending on the laser power and the developing time of the photoresist. (A) of FIG.
Indicates a case where the laser power is large, and (b) indicates a case where the laser power is small. Generally, when the laser power is large, the pits are long and the edges are sharp, and when the development time is long, the pits are long. FIG. 7 shows the relationship between the laser power and the amount of asymmetry.

Conventionally, when reproducing a disk duplicated from a stamper in a molding process, in order to obtain the best electrical characteristics, that is, to obtain optimum asymmetry, it is necessary to control the laser power applied to the glass master. The development time was controlled or either method was used. However, even if the laser power or the development time is controlled to match the optimal asymmetry value, other necessary factors such as the degree of modulation may be affected by the size of the laser beam for exposure or the shape of the laser beam. In some cases, a stamper having pits satisfying electrical characteristics cannot be produced. Also, even if it is possible, the pit edges are steep, so the profiling (PL
OWING), the releasability from the mold was poor, and the stamper was difficult to mold. Further, if the laser power is unnecessarily increased or the developing time is lengthened, the width of the pits to be formed becomes wider, which causes a problem with a disk having a high recording density.

[0007]

The parameter that can be controlled to produce a stamper having an optimum pit shape is the laser power or the development time. However, the present invention relates to another parameter that can be controlled, namely, the modulation to be recorded. By adding the control of the on / off timing of the digital signal to the control of the exposure time of the photoresist at the time of ON, it is easy to obtain an optimum pit shape.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a disk in which pits are formed and a signal is recorded by irradiating a laser beam on and off a photoresist coated master to form a pit and record a signal. Changing the on / off ratio of the digital signal from 50:50, that is,
A pit shape control method for a disc, characterized by controlling the exposure time of a glass master coated with a photoresist at the time of ON.

Further, the present invention provides a laser oscillator, an optical modulator for turning on / off light emitted from the laser oscillator, a digital signal modulator for modulating a digital signal to be recorded, and an on / off switch for the modulated digital signal. A duty controller for changing the timing by a predetermined amount, and an optical modulator driving circuit for driving the optical modulator according to an output signal from the duty controller, and the modulated digital signal to be recorded is turned on and off by the duty controller. Change the ratio from 50:50, ie
A disk recording apparatus characterized in that the exposure time to a glass master coated with a photoresist during ON is controlled.

To change the duty of the modulated digital signal input to the optical modulator driving circuit for driving the optical modulator, in other words, to lengthen or shorten the ON time of the light for exposing the glass master. By combining conventional control of laser power or control of development time, an optimum pit shape can be easily obtained. For example, as shown in FIG. 7, when the duty of the output signal of the digital signal modulator is 50:50, the laser power is a
The optimum asymmetry was obtained with mw (milliwatt), but when the pit edge is steep and the formability is poor, the following method is available. By making the laser power smaller than amw and instead lengthening the time that the laser is on, that is, by changing the duty, optimal asymmetry can be maintained, and the edges of the pits become smoother and the formability is reduced. Get better.

To change the duty of the modulated digital signal input to the optical modulator driving circuit, a duty controller is inserted between the digital signal modulator and the optical modulator driving circuit as shown in FIG. , Off ratio from 50:50.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Digital video disks (DVDs)
= (Product name), the duty was changed after 8-16 modulation, the optimum pit shape was easily obtained, and a stamper with good moldability was obtained. For other applications, the same is possible after 8-14 modulation of a compact disc (CD = trade name).

FIG. 1 schematically shows a disk recording apparatus according to an embodiment of the present invention. Light emitted from a laser oscillator 1 passes through an optical lens 2 and is turned on and off by an optical modulator 3. The light passes through several optical elements and then passes through an objective lens 4 to a glass master 5 coated with photoresist. Irradiation exposes the photoresist. This configuration is the same as the conventional disk recording device. On the other hand, digital data to be recorded is modulated by a digital modulator 6 such as adding an error correction code, and then input to the duty controller 8. The duty controller 8 controls a digital signal as shown in FIG. In FIG. 2, α indicates the length of the signal level H side (laser light on state), β indicates the length of the signal level L side (laser light off state), (a) indicates the signal before control, b) is an output signal with a longer α control (longer laser beam ON state and longer pit length), and (c) is an output signal with shorter α control (short laser light ON state and shorter pit length). Is shown. The output signal from the duty controller 8 is sent to the optical modulator driving circuit 7, and the optical modulator operates according to the digital signal controlled as described above, and the laser light is turned on and off.

FIGS. 3 to 5 are explanatory diagrams showing an example of the duty controller 8. FIG. Duty controller 8
Is composed of a circuit 1 (H-side pulse shortening circuit) and a circuit 2 (H-side pulse enlargement circuit). Circuit 1 has a delay line and N
The pulse on the pit side (signal level H side) is shortened (see FIG. 4B). The circuit 2 includes a delay line, a duty select switch, and a NAND, and can be expanded to an arbitrary pulse width by the select switch (see FIG. 4C). Therefore, the duty controller 8 can freely control the basic digital signal (the digital signal subjected to the EFM modulation in the embodiment) in the selection range of FIG.

FIG. 5 (A) shows a pulse on the pit side of 10n.
This is an example in which s (nanosecond) is enlarged. The fall of the pulse is delayed by 10 ns by the delay line of the circuit 1. The delay amount of the circuit 1 is fixed at 10 ns.
Next, the pulse is inverted by the NAND of the circuit 1. Circuit 1
Is input to the delay line of the circuit 2, but the circuit 2 can arbitrarily change the delay amount by a select switch within the range of 0 to 20 ns. In this case, the delay amount is set to 0. The delay output of circuit 2 is the NAND of circuit 2
The NAND output of the circuit 2 has a pulse on the pit side expanded by 10 ns (nanosecond) compared to the basic EMS signal.

FIG. 5B shows an example in which the duty control amount is set to zero. The delay output and the NAND output of the circuit 1 are the same as those in FIG. 1A, but the delay amount of the circuit 2 is set to 10 ns, and as a result, the NAND output of the circuit 2 has a duty control amount of 0.

FIG. 5C shows that the pulse on the pit side is 10n.
This is an example of shortening s (nanosecond). The delay output and the NAND output in the circuit 1 are also the same as those in (A), but the delay amount of the circuit 2 is set to 20 ns. As a result, the pit side pulse of the NAND output of the circuit 2 is 10 ns compared to the basic EMS signal. (Nanosecond) It is shortened.

In the duty controller 8 of this embodiment, the delay amount of the circuit 1 is fixed at 10 ns, and the delay amount of the circuit 2 can be selected in the range of 0 to 20 ns in units of 2 ns. Therefore, the control amount of the duty controller is -10 to +10 ns. Can be set in units of 2 ns. Of course, the configuration of the duty controller is not limited to this example, and any configuration can be used as long as the pulse width can be arbitrarily controlled.

[0019]

According to the present invention, the number of control parameters for manufacturing a stamper in the process of manufacturing a disc increases,
It becomes easier to obtain the optimum pit shape of the disc. Further, since only the pit length can be changed by controlling the duty, the pit edge can be made smooth by setting the laser power small, and the formability of the disc can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a disk recording device according to an embodiment.

FIG. 2 is an explanatory diagram of a duty control.

FIG. 3 is an explanatory diagram of a duty controller 8;

FIG. 4 is an explanatory diagram of a duty controller 8;

FIG. 5 is an explanatory diagram of a duty controller 8;

FIG. 6 is an explanatory diagram of a conventional disk recording device.

FIG. 7 is an explanatory diagram showing a relationship between asymmetry and laser power.

FIG. 8 is an explanatory diagram of the concept of asymmetry.

FIG. 9 is an explanatory diagram showing a relationship between laser power and a pit shape.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Optical lens 3 Optical modulator 4 Objective lens 5 Glass master 6 Digital signal modulator 7 Optical modulator drive circuit 8 Duty controller 11 Laser oscillator 12 Optical lens 13 Optical modulator 14 Objective lens 15 Glass master 16 Digital signal modulation Device 17 Optical modulator drive circuit

Claims (2)

[Claims] 1. A method for manufacturing a disk in which a pit is formed and a signal is recorded by irradiating a laser beam on and off to a master on which a photoresist has been applied, and turning on and off a modulated digital signal to be recorded. A pit shape control method for a disk, wherein the ratio is changed from 50:50 to control the exposure time of a glass master coated with a photoresist when it is turned on. 2. A laser oscillator, an optical modulator for turning on and off light emitted from the laser oscillator, a digital signal modulator for modulating a digital signal to be recorded, and a timing for turning on and off the modulated digital signal. A duty controller that changes the amount by a predetermined amount; and an optical modulator driving circuit that drives the optical modulator in accordance with an output signal from the duty controller. : A disk recording device, wherein the exposure time to a glass master coated with a photoresist at the time of ON is controlled by changing from 50.