JP2001325728A - Device for manufacturing master disk of optical disk, method for manufacturing master disk of optical disk and optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for manufacturing a master disk of an optical disk capable of forming a pit having a fixed pit width without depending on pit strength. SOLUTION: A format signal source 106 which generates a clock signal at a fixed period T, and a laser 101, an EO stabilizer 102 and an EO modulator 103 which generate a laser pulse beam using the period T as a reference are provided in the device for manufacturing the maser disk of the optical disk. The intensity P of the laser pulse beam is corrected into intensity P (nT) based on the following formula by the EO modulator 103. P (nT)=a.n-b×P (min), where 1.1<=a<=1.4, 0.15<=b<=0.30, and P (min) is the intensity of the laser when the shortest pit pattern is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk master manufacturing apparatus and an optical disk master manufacturing method, and more particularly to an optical disk master and an optical disk master manufacturing method for forming pits using an exposure process using a laser beam as a light source. And optical disks.

[0002]

2. Description of the Related Art Holes (pits) in which ROM information is recorded are provided on the surface of a read-only disk (ROM disk). A substrate used for an optical disk is produced by duplicating a stamper. The stamper is manufactured from a master on which pits and tracking guide grooves are formed by using a high-precision optical exposure apparatus (laser cutter). The master disc of the optical disc has a resist pattern for forming pits and a resist pattern for forming a guide groove for tracking formed on a glass substrate. The resist pattern is formed by exposing a photoresist applied on a glass substrate to a light beam such as a laser beam. The stamper is manufactured by further providing a back plate on a die obtained by depositing a metal film on a resist pattern formed on a master.

[0003] In the exposure process at the time of producing a master, a light beam is modulated according to ROM information to be recorded, and becomes a pulse light in which a high output and a low output are alternately repeated. The pulse light repeats high output and low output with reference to the cycle T of the clock signal (base clock) generated by the clock signal generator. Then, a pit forming resist pattern having a length corresponding to the high output time and a space having a length corresponding to the low output time are alternately formed.

[0004] The light beam modulation method includes, for example, EFM.
(Eight to Fourteen Modulation). In the EFM method, a high output and a low output of the pulse light are repeated at a period of 3T to 11T. Therefore, E
In the exposure by the FM method, a resist pattern or space for forming a pit having a length corresponding to time 3T to time 11T can be formed on the optical disk master.

[0005] The jitter characteristics of a ROM disk deteriorate when the pit length of the substrate used for the disk is non-uniform. For this reason, for example, Japanese Patent Application Laid-Open No. 10-3
There is a technique for reducing the difference between the logical pit length and the actually formed pit length as in the inventions described in JP-A-3467 and JP-A-10-33468. The invention described in JP-A-10-33467 reduces the light intensity immediately after the rising and falling of the pulse light in the exposure step.
The invention described in Japanese Patent Application Laid-Open No. 8 (1995) No. 8 discloses exposing a resist pattern for forming pits with a pulse train in which a high output and a low output are repeated at a cycle shorter than the basic clock.

[0006]

By the way, pits of various lengths are present on a substrate of an optical disk according to ROM information to be recorded. However, in the above-described prior art, the pulse light is controlled regardless of the pit length to be formed. For this reason, the prior art has an effect when forming a pit having a pit length within a certain range, but obtains a sufficient effect when forming a pit having a length longer than a certain range. Can not do.

The jitter characteristics of an optical disk are affected not only by the uniformity of the pit length but also by the pit width (the length of the pit along the radial direction of the optical disk). The pits have a constant pit width regardless of the change in the pit length, and the shape (aspect ratio) changes with the change in the pit length. For this reason, it is conceivable that the optimum exposure conditions for producing a resist pattern for forming pits vary depending on the pit length. However, the control of the light beam in the exposure step does not consider the pit width, and the longest pit (longest pit) and the shortest pit (shortest pit) among the pits included in the pit row formed on the optical disk substrate. And the pit width may differ.

The difference in pit width appears as a phenomenon in which the pit width of a relatively short pit becomes narrower than the pit width of a relatively long pit. A pit having a width smaller than a predetermined value cannot reproduce an RF signal having a sufficient amplitude, thereby deteriorating jitter characteristics of the optical disc. In addition, when the pit width varies in the pit row, a phenomenon occurs in which the center of the signal amplitude obtained by reproducing the pit is shifted by the pit length and the jitter characteristic of the optical disc is deteriorated.

The present invention has been made in view of the above points, and has been made by correcting the intensity of the laser pulse light, or the on-time (exposure time) and the off-time according to the length of the pit to be formed. It is an object of the present invention to provide an optical disk master manufacturing apparatus and an optical disk master manufacturing method capable of forming pits having dimensions and shapes according to data regardless of the length.

Further, the present invention limits the ratio of the pit width of the longest pit to the pit width of the shortest pit among the pits included in the pit row, and reproduces a reproduced signal having good jitter characteristics regardless of a change in the pit length. It is an object of the present invention to provide an optical disk capable of obtaining the above. It is another object of the present invention to provide an optical disk in which the amplitude centers of reproduced signals obtained from pits match regardless of the change in pit width. Furthermore, the present invention
It is an object of the present invention to provide an optical disk capable of obtaining a reproduced signal having good jitter characteristics regardless of a change in duty ratio.

[0011]

The above objects can be attained by the following means. That is, the invention according to claim 1 is an optical disc master manufacturing apparatus for forming a pattern for forming pits using an exposure process using a laser beam as a light source, wherein the clock signal generates a clock signal at a constant cycle T. Generating means, pulse light generating means for generating a laser pulse light having an exposure time nT times an integer (n) times the period T, and intensity P (nT) of the laser pulse light having a time nT as the exposure time And a light intensity correcting means for correcting the light intensity by the following equation. P (nT) = a · n ^−b × P (min) 1.1 ≦ a ≦ 1.4 0.15 ≦ b ≦ 0.30 P (min): laser intensity at the time of forming the shortest pit pattern

With this configuration, the optical disk master manufacturing apparatus can control the intensity of the laser pulse light according to the exposure time, that is, the length of the pit pattern to be formed. Therefore, a pit pattern can be formed under appropriate exposure conditions according to the length of the pit pattern.

According to a second aspect of the present invention, the laser light is a spot light having a circular cross section with a diameter d, and the pulse light has a pit pattern having a length of 10 times or more of d. when forming, the exposure time nT of the laser pulse light, and is characterized in further comprising an exposure time correction means for correcting the exposure time by the equation nT _c below. nT _c = (n + a) T 1.0 ≦ a ≦ 2.0

With this configuration, the optical disk master manufacturing apparatus can control the exposure time of the laser pulse light according to the length of the pit pattern to be formed. Therefore, a pit pattern can be formed under appropriate exposure conditions even for a relatively long pit pattern (10 times or more the laser beam cross section d).

According to a third aspect of the present invention, there is provided a method of manufacturing a master optical disk for forming a pit pattern for forming a pit by using an exposure process using a laser beam as a light source, wherein an integer of a period T of a clock signal is used. A pulse light generation step of generating a laser pulse light having an exposure time of n) times the time nT, and the intensity P (nT) of the laser pulse light generated using the time nT as the exposure time are corrected by the following equation. And a light intensity correction step. P (nT) = a · n ^−b × P (min) 1.1 ≦ a ≦ 1.4 0.15 ≦ b ≦ 0.30 P (min): laser intensity at the time of forming the shortest pit pattern

With this configuration, the intensity of the laser pulse light can be controlled according to the exposure time, that is, the length of the pit pattern to be formed. Therefore, a pit pattern can be formed under appropriate exposure conditions according to the length of the pit pattern.

According to a fourth aspect of the present invention, the laser light is a spot light having a circular cross section with a diameter d, and the pulse light generated in the pulse light generating step is ten times as large as d. when forming the above length of the pit pattern, the exposure time nT of the laser pulse light, and is characterized in further comprising an exposure time correction step of correcting the exposure time nT _c by the following equation. nT _c = (n + a) T 1.0 ≦ a ≦ 2.0

With this configuration, the exposure time of the laser pulse light can be controlled according to the length of the pit pattern to be formed. Therefore, a pit pattern can be formed under appropriate exposure conditions even for a relatively long pit pattern (10 times or more the laser beam cross section d).

According to a fifth aspect of the present invention, there is provided an optical disk constituted by using a substrate on which a pit row is formed, wherein the shortest pit having the shortest length among the pits included in the pit row is provided. The width W1 and the width W2 of the longest pit having the longest length are in a relationship of W1 / W2 = 0.8 to 1.2.

With this configuration, the deviation of the amplitude center between the reproduced signal obtained from the shortest pit and the reproduced signal obtained from the longest pit can be suppressed to an allowable range.

According to a sixth aspect of the present invention, the width W of the pits included in the pit row and the track pitch Tp in the pit row have a relationship of 0.3 Tp ≦ W ≦ 0.7 Tp. It is characterized by the following.

With this configuration, the track pitch and the pit width can be set to an appropriate relationship to obtain a reproduced signal having a sufficient amplitude, regardless of the track pitch and the pit width.

According to a seventh aspect of the present invention, the length Pl of the pits included in the pit row and the space length Ps between the pits in the pit row are Pl / (Pl + Ps) = 0.4 to 0.4. 0.6.

With this configuration, the difference between the pit width of the shortest pit and the pit width of the longest pit is suppressed,
The deviation of the amplitude center between the reproduction signal obtained by the shortest pit and the reproduction signal obtained by the longest pit can be suppressed to an allowable range.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in the order of Embodiment 1 and Embodiment 2.

(Embodiment 1) FIG. 1 is a block diagram for explaining an optical disk master manufacturing apparatus according to Embodiment 1. The optical disk master manufacturing apparatus according to the first embodiment is an optical disk master manufacturing apparatus that forms a resist pattern (pit pattern) for forming pits using an exposure process using a laser beam as a light source.
01, EO (Electric O) that stabilizes the generated laser light
ptics) Stabilizer 102, EO modulator 103 for controlling on / off of laser light, and laser light to glass substrate 10
5 has a light head 104 for irradiation.

The EO modulator 103 is connected to a format signal source 106 that generates a clock signal at a constant cycle T, and changes the intensity of the laser beam with reference to the cycle T of the clock signal, that is, an integer multiple of the cycle T. The laser light is turned on or off at every time nT to turn the laser light into laser pulse light. The EO modulator 103 inputs pit data (pit data) to be formed on the optical disk substrate from a control unit (not shown), controls the intensity of the laser pulse light according to the input data, and further turns on the laser pulse light. Control off time. The control of the intensity of the laser pulse light and the on / off time will be described later in detail.

After the surface of the glass substrate 105 is polished and cleaned, a photoresist is spin-coated, and further baked in a clean open at 90 ° C. for 30 minutes. The photoresist thickness after baking is about 8
0 nm. The glass substrate 105 is attached to a jig (not shown) and is rotated at a constant rotation speed.

On the other hand, the laser 101 emits laser light having a wavelength of 413 nm from a Kr ⁺ laser tube. After passing through the EO stabilizer 102 and the EO modulator 103, the laser beam can be expanded in beam diameter by a beam expander (not shown). The optical head 104 has an objective lens with NA = 0.9. The laser light guided to the optical head 104 is condensed by this objective lens, and the laser pulse light 1 having a circular cross section diameter d (spot diameter) of 0.5 μm.
Is irradiated on the photoresist on the rotating glass substrate 105. The laser light exposes the photoresist when turned on to form a resist pattern (pit pattern) for pit formation. On the other hand, when turned off, the photoresist is not exposed, and a space is formed between the pit patterns.

The optical head 104 is mounted on the glass substrate 10.
Each time 5 rotates once, it moves a fixed distance (track pitch) to form a latent image of a pit pattern for one track. The optical disk master manufacturing apparatus according to the first embodiment has an exposure linear velocity of 3.5 m / s and a track pitch of 0.74.
An EFM random pattern was created under the condition of μm. After the processing described above, when the unexposed portion of the resist is removed with a developing solution, a pit pattern on the glass substrate 105,
Alternatively, the resist pattern for forming the tracking groove remains, and the master disk of the optical disk is completed.

FIG. 2 is a diagram for explaining an optical disk master manufactured by the optical disk master manufacturing apparatus shown in FIG. FIG. 2A is a surface view of the master optical disc,
FIG. 2B is a cross-sectional view of the master optical disc shown in FIG. 2A along the broken line AB shown in the drawing. As shown, a plurality of pit patterns 2 corresponding to the pit data are formed on the surface of the master optical disc. In this specification, a set of a plurality of pit patterns is called a pit pattern row, and a set of pits formed by the pit pattern row is called a pit row.

In this specification, the length of a pit pattern along the track direction of the master optical disc is referred to as the pit pattern length of the pit pattern (indicated by L in the figure), and the length of the pit pattern along the radial direction of the master optical disc. The length is called the pit pattern width of the pit pattern (indicated by W in the figure).
The interval between the pit patterns adjacent to each other in the track direction is called a pattern space S, and the pitch of the pit patterns adjacent to each other in the radial direction is called a pattern track pitch (indicated by PTp in the figure).

Hereinafter, in this specification, the on-time of the laser pulse light 1 when forming one pit pattern is referred to as an exposure time. The exposure time is represented as nT because it is an integral multiple of the cycle T of the clock signal generated by the format signal source 106. In the embodiment of the present invention, the rotation speed of the glass substrate 105 and the moving speed of the optical head 104 are fixed, and the pit pattern length L is substantially proportional to the exposure time. Further, the intensity of the laser beam at the time of exposure for the exposure time nT is represented by P (nT).

Next, the control of the intensity of the laser pulse light, which is performed by the optical disk master manufacturing apparatus of the first embodiment,
Control of exposure time by laser pulse light will be described. Control of Laser Pulse Light Intensity In the optical disk master manufacturing apparatus of the first embodiment, the EO modulator 103 determines the intensity P of the laser pulse light 1 whose exposure time is a time nT, which is an integer (n) times the period T, as follows: Is corrected to the intensity P (nT) by the equation (1). P (nT) = a · n ^−b × P (min) (1) where, in the expression (1), the value of a is 1.1 to 1.4.
(1.1 ≦ a ≦ 1.4), and the value of b is 0.15 to
0.30 (0.15 ≦ b ≦ 0.30). And
Embodiment 1 in which a random pattern is created by the EFM method
Is the intensity P (3T) of the laser pulse light 1 when the resist pattern is formed in 3T which is the shortest exposure time.

FIG. 3 is a diagram showing the relationship between the exposure time of the laser pulse light 1 for forming the pit pattern and the intensity P of the laser pulse light 1. The exposure time of the laser pulse light 1 depends on the pit of the pit pattern. It is proportional to the length. The horizontal axis in FIG. 3 shows the exposure time of the laser pulse light 1 as a ratio when the period T (second) of the signal generated by the format signal source 106 is 1. The vertical axis represents the intensity P (nT) when the exposure time of the laser pulse light 1 is nT, and the intensity P
It is shown as a ratio when (3T) is set to 1. In FIG. 3, black squares indicate data when a pit pattern having a pit width of 0.15 μm is formed, plots □ indicate data when a pit pattern having a pit width of 0.20 μm is formed, and plots △ indicate pits. The data when a pit pattern having a width of 0.35 μm is formed are shown.

The relationship between the exposure time nT and the intensity P (nT) of the laser pulse light 1 shown in FIG. 3 is expressed by equation (1) '. P (nT) = a · n− ^b × P (3T) (1) ′ In the first embodiment, the curve represented by the equation (1) ′ is used as a laser intensity correction curve, and the EO modulator 103 Time nT
The intensity P (nT) is corrected using the laser intensity correction curve in accordance with Note that the value of a and the value of b in the equation (1) ′ vary depending on the characteristics of the photoresist and the exposure linear velocity. However, the pit width is 0.15 to 0.35μ
In the range of m, by setting the value of a to 1.1 to 1.4 and the value of b to 0.15 to 0.30, a pit pattern having a uniform pit pattern width regardless of the exposure time nT Can be formed.

It should be noted that the curve C shown in FIG.
This is a laser intensity correction curve for forming a 2 μm pit pattern, where a has a value of 1.2 and b has a value of 0.21.

FIG. 4 is a diagram for explaining the intensity correction of the laser pulse light 1 based on the laser intensity correction curve. The horizontal axis of FIG. 4 indicates the exposure time (second) of the laser pulse light 1, and the vertical axis indicates
The intensity of the laser pulse light 1 is normalized and shown. In the first embodiment, the laser light intensity is set such that the maximum intensity of the laser pulse light 1 at each exposure time matches the laser light intensity on the laser intensity correction curve.

FIG. 5 is a view for explaining the results of actually measuring the pit width of an optical disk substrate prepared using an optical disk master having a pit pattern formed by the laser pulse light 1 whose intensity is set by the method shown in FIG. is there. The horizontal axis in FIG. 5 shows the exposure time (second) at the time of forming the pit pattern, and the vertical axis shows the pit width (μm) of the pit actually measured by AFM (Atomic Force Microscopy).

FIG. 5 shows that the pit width is formed at a substantially constant value regardless of the exposure time in the range of the exposure time of 3T to 14T seconds. Since the exposure time is proportional to the pit length, it can be said that the first embodiment can provide an optical disk substrate having pits having a uniform width regardless of the pit length.

Further, the inventors of the present invention manufactured an optical disk substrate from the optical disk master manufactured by the optical disk master manufacturing apparatus of the first embodiment. Then, an Al reflective film is formed on the optical disk substrate to produce an optical disk, and a laser beam having a wavelength of 650 nm is irradiated with NA = 0.60.
Reproduction was performed at a reproduction linear velocity of 3.5 m / s while condensing with the objective lens of No. 1. As a result of reproduction, a reproduced signal having a jitter of 7.4% was obtained from pits having a pit width of 0.32 μm.
Today, since the jitter allowed in the DVD (Digital Versatile Disc) standard is 8%, the 7.4% jitter can be said to be sufficiently low.

Control of Exposure Time of Laser Pulse Light FIG. 6 shows an exposure time for forming a pit pattern and a duty ratio of the formed pit pattern (pit pattern length / (pit pattern length + pattern space length ( It is a figure which shows the relationship with pattern space length))).
The horizontal axis in FIG. 6 indicates the exposure time by the laser pulse light 1 and the period T (second) of the signal generated by the format signal source 106.
Is set to 1 and the ratio is shown. The vertical axis indicates the duty ratio of the pit pattern.

The plot ◆ shown in FIG. 6 is the data when a pit pattern was formed using the laser pulse light 1 having the spot diameter d1. The plot ○ is the laser pulse light having the spot diameter d2. The data when a pit pattern is formed using No. 1 and the plots ● indicate the data when a pit pattern is formed using a laser pulse light 1 having a spot diameter of d3. For spot diameter d1, spot diameter d2, and spot diameter d3, d1> d
2> d3. It is also assumed that the duty ratio shown in FIG. 6 is set to a constant value regardless of the pit pattern length (the pit pattern length and the pattern space length always have the same value).

According to FIG. 6, the exposure time is long, that is,
It can be seen that when a relatively long pit pattern is formed, the duty ratio of the formed pit pattern is smaller than a shorter pit pattern. Such a change in the duty ratio of the pit pattern due to the pit pattern length occurs because a pit pattern having a relatively long pit pattern length tends to be formed shorter than the pit data.

In the optical disk master manufacturing apparatus of the first embodiment, in order to suppress a change in the duty ratio due to the pit pattern length, the laser pulse light 1 forms a pit pattern having a length of 10 times or more the spot diameter d of the laser pulse light 1. when forming, the exposure time nT according to the laser pulse light, and shall be corrected to the exposure time nT _c by the following equation. nT _c = (n + a) T (2)

FIG. 7 is a diagram schematically showing the correction of the exposure time nT by the equation (2), and shows that the exposure time nT is corrected to (n + a) by the above equation (2). I have. Although the value of a in the formula (2) varies depending on the characteristics of the photoresist and the exposure conditions, in the embodiment of the present invention, the value of a is 1.0 or more and 2.0 or less (1.0 ≦ a ≦
2.0) is desirable.

FIG. 8 is a view for explaining the results of actual measurement of the pit width of an optical disk substrate produced using an optical disk master having a pit pattern formed by the laser pulse light 1 whose exposure time has been corrected by the method shown in FIG. It is. The horizontal axis in FIG. 8 indicates the exposure time (second) at the time of forming the pit pattern, and the vertical axis indicates the duty ratio of the pit actually measured by the AFM (pit length / (pit length + space length (space length))). Is shown.

FIG. 8 shows the exposure time 3T of the laser pulse light 1.
In the range of ~ 11T seconds, the duty ratio of the pit is
It shows that it has a substantially constant value regardless of the exposure time. The exposure time by the laser pulse light is proportional to the pit length, and the change in the duty ratio is proportional to the difference between the pit length on the pit data and the actually formed pit length.
Therefore, in the first embodiment in which the exposure time by the laser pulse light 1 is corrected, it can be said that pits having the pit length according to the pit data can be formed on the optical disk substrate regardless of the pit length on the pit data.

Further, the inventors of the present invention corrected the exposure time by the laser pulse light by the method shown in FIG. 7 and manufactured an optical disk master by the optical disk master manufacturing apparatus of the first embodiment. Further, an optical disk substrate was manufactured from the master optical disk, and an Al reflective film was formed on the optical disk substrate to manufacture an optical disk. Then, as a result of reproducing the manufactured optical disk, a reproduced signal having a jitter of 7.1% was obtained from pits having a pit width of 0.32 μm and a duty ratio of 0.45. Today, since the jitter allowed by the DVD standard is 8%, the 7.1% jitter is:
It can be said that it is sufficiently low.

As described above, according to the invention of the first embodiment, an optical disk master manufacturing apparatus and an optical disk master manufacturing method capable of forming a pit pattern having a uniform pit pattern width regardless of the length of the pit pattern are provided. can do. Further, it is possible to provide an optical disk master manufacturing apparatus and an optical disk master manufacturing method capable of forming a pit pattern having a length of 10 times or more the diameter d of the laser beam cross section according to the design length.

The optical disk master manufacturing apparatus and the optical disk master manufacturing method according to the first embodiment can manufacture an optical disk substrate having pits having a uniform pit width irrespective of the pit length. It is possible to provide a simple optical disk. Furthermore, the optical disk master manufacturing apparatus and the optical disk master manufacturing method according to the first embodiment can manufacture an optical disk substrate having relatively designed pit lengths even for relatively long pits, thereby providing an optical disk having good jitter characteristics. can do.

(Embodiment 2) Next, an optical disc according to Embodiment 2 of the present invention will be described. The optical disk according to the second embodiment is an optical disk configured using a substrate on which a pit row is formed. The pit width and the duty ratio of the pits are defined in order to provide an optical disk in which the pit width of the pits included in the pit row is uniform and a good reproduction signal with little jitter is obtained from the pits. .

Hereinafter, the pit width of the pits included in the pit row in the optical disc according to the second embodiment will be defined.
The definition of the relationship between the pit width and the track pitch and the definition of the duty ratio will be described. The optical disk of the second embodiment is manufactured by forming a reflective film of Al on an optical disk substrate manufactured from the optical disk master of the first embodiment. 0.45μ on the surface of the optical disk substrate
An EFM random pattern is formed at a track pitch of m. The reproduction of the optical disk is performed at a wavelength of 400 nm.
Was condensed by an objective lens with NA = 0.60 and performed at a reproduction linear velocity of 3.5 m / s.

Definition of pit width of pit included in pit row The difference between the shortest pit width and the longest pit width is determined by the center of amplitude between the shortest pit signal obtained by the shortest pit and the longest pit signal obtained by the longest pit. It may cause deviation.
It is known that when the deviation amount of the amplitude center becomes large, the threshold value for binarizing the reproduction signal is shifted between the shortest pit and the longest pit, causing an error in reading information from the optical disk and increasing jitter.

For this reason, the optical disk of the second embodiment
Relationship between the width W1 (shortest pit width) of the pit having the shortest pit length (shortest pit) and the width W2 (longest pit width) of the pit having the longest pit length (longest pit) of the pits included in the pit row W1 / W2 = 0.8 to 1.2 (3)

FIG. 9 is a diagram showing the relationship between the ratio of the shortest pit width W1 to the longest pit width W2 and the jitter of the reproduction signal obtained from the optical disk. The horizontal axis in FIG. 9 indicates the shortest pit width / the longest pit width, and the vertical axis indicates the jitter contained in the reproduction signal of the optical disk, and the format signal source 1
06 is expressed as a percentage of the signal generated.

According to FIG. 9, the jitter is expressed by the shortest pit width /
It can be seen that the longest pit width is 1 when the shortest pit width and the longest pit width have the same pit width, and becomes larger as the difference in pit width becomes larger. And the shortest pit width / longest pit width is 0.8 ~
If it is 1.2, the jitter is found to be an acceptable value. In the second embodiment, the allowable jitter of the DVD standard is 8%, so the allowable value of the jitter is set to 8% or less.

Definition of Relationship between Pit Width and Track Pitch In the optical disc of the second embodiment, the relationship between the width W of the pits included in the pit row and the track pitch Tp in the pit row is 0.3 Tp ≦ W ≦ 0. 0.7 Tp (4)

FIG. 10 is a diagram showing the relationship between the pit width and the 3T modulation degree with respect to the track pitch. The 3T modulation degree is a value represented by a ratio between the amplitude of the shortest pit formed by the EFM modulation method and the level of the ON signal of the longest pit,
This value is an index of the amplitude of the reproduction signal. The shortest pit in the EFM modulation method has an exposure time of laser pulse light of 3
This is a pit formed from a pit pattern formed as T. The longest pit is a pit formed from a pit pattern formed by setting the exposure time of the laser pulse light to 14T. The horizontal axis in FIG. 10 shows the pit width as a multiple of the track pitch, and the vertical axis shows the 3T modulation.

[0060] Today, the DVD standard states that a reproduced signal having an amplitude sufficient for reproduction can be obtained when the 3T modulation degree is 15% or more. Therefore, Embodiment 2
In this case, the pit width at which a 15% or more 3T modulated signal is obtained is defined as the pit width of the optical disk. According to FIG.
It can be seen that a 3T modulation degree of 5 or more is obtained when the pit width is 0.4 to 0.6 times the track pitch.

Definition of Duty Ratio As described above, the shift between the shortest pit width and the longest pit width causes a shift in the center of the amplitude between the shortest pit signal and the longest pit signal, resulting in information reading error and jitter on the optical disk. Contribute to the increase in The difference between the shortest pit width and the longest pit width is affected by the pit duty ratio,
There is a certain range in the duty ratio in which the pit width can be formed to be constant regardless of the pit length.

For this reason, the optical disk of the second embodiment
The length P1 of the pits included in the pit row and the space length Ps between the pits in the pit row are set as Pl / (Pl + Ps) = 0.4 to 0.6 (4).

FIG. 11 is a diagram showing the relationship between the duty ratio of the pits provided on the optical disc (pit length / (pit length + space length)) and the jitter of the reproduction signal obtained from the optical disc. In FIG. 11, the horizontal axis represents the duty ratio, and the vertical axis represents the jitter contained in the reproduced signal of the optical disk as a percentage of the signal generated by the format signal source 106 in%. According to FIG. 11, it can be seen that the jitter becomes an allowable value when the pit duty ratio is 0.4 to 0.6. Note that FIG.
Also, the allowable value of the jitter is set to 8% or less.

As described above, according to the second embodiment, it is possible to provide an optical disc capable of obtaining a reproduced signal having a sufficient amplitude regardless of a change in the pit length in the optical disc. Further, according to the second embodiment, it is possible to provide an optical disc capable of obtaining a reproduced signal having the same amplitude center regardless of a change in the pit width. Further, according to the second embodiment, it is possible to provide an optical disc capable of obtaining a reproduction signal having the same amplitude center regardless of a change in the duty ratio in the optical disc.

[0065]

As described above, the present invention has the following effects. That is, the invention according to claim 1 is an optical disk capable of forming a pit pattern having a uniform pit pattern width regardless of the pit pattern length by correcting the intensity of the laser pulse light according to the pit length to be formed. A master production apparatus can be provided.

According to the second aspect of the present invention, a relatively long pit pattern (10 times or more the diameter d of the laser beam cross section) is designed by correcting the exposure time of the laser pulse light according to the pit length to be formed. It is possible to solve the problem of not being formed as described. Further, it is possible to provide an optical disk master manufacturing apparatus capable of forming a pit pattern as designed irrespective of the length of the pit pattern.

According to the third aspect of the present invention, a pit pattern having a uniform pit pattern width can be formed irrespective of the pit pattern length by correcting the intensity of the laser pulse light according to the pit length to be formed. An optical disk master manufacturing method can be provided.

According to a fourth aspect of the present invention, a relatively long pit pattern (10 times or more the diameter d of the laser beam cross section) is designed by correcting the exposure time by the laser pulse light according to the pit length to be formed. It is possible to solve the problem of not being formed as described. Further, it is possible to provide a method for manufacturing an optical disc master capable of forming a pit pattern as designed irrespective of the length of the pit pattern.

According to the fifth aspect of the present invention, the ratio between the pit width of the longest pit and the pit width of the shortest pit among the pits included in the pit row is limited, and the ratio is sufficient regardless of the change in the pit length in the optical disk. It is possible to provide an optical disc capable of obtaining a reproduced signal having an appropriate amplitude.

According to a sixth aspect of the present invention, there is provided an optical disk capable of limiting a width of a pit included in a pit row and a track pitch and obtaining a reproduced signal whose amplitude center coincides regardless of a change in a pit width in the optical disk. Can be provided.

According to a seventh aspect of the present invention, there is provided an optical disc in which a duty ratio of pits included in a pit row is limited, and a reproduced signal having the same amplitude center is obtained irrespective of a change in the duty ratio in the optical disc. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an optical disk master manufacturing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an optical disc master manufactured by the optical disc master manufacturing apparatus shown in FIG. 1;

FIG. 3 is a diagram showing a relationship between an exposure time by a laser pulse light for forming a pit pattern and an intensity of the laser pulse light.

FIG. 4 is a diagram for explaining intensity correction of laser pulse light based on a laser intensity correction curve.

FIG. 5 is a view showing the results of actually measuring the pit width of an optical disk substrate formed using an optical disk master on which a pit pattern is formed by laser pulse light whose intensity is set by the method shown in FIG.

FIG. 6 is a diagram showing a relationship between an exposure time of a laser pulse light for forming a pit pattern and a duty ratio of a pit pattern formed by the laser pulse light.

FIG. 7 is a diagram schematically showing correction of exposure time by laser pulse light.

8 is a diagram showing the results of actually measuring the pit width of an optical disk substrate produced using an optical disk master having a pit pattern formed by laser pulse light whose period has been corrected by the method shown in FIG. 7;

FIG. 9 shows the ratio of the shortest pit width to the longest pit width,
FIG. 3 is a diagram showing a relationship between a reproduction signal obtained from an optical disc and jitter.

FIG. 10 is a diagram showing a relationship between a pit width and a 3T modulation degree with respect to a track pitch.

FIG. 11 is a diagram illustrating a relationship between a duty ratio of a pit provided on an optical disc and a jitter of a reproduction signal obtained from the optical disc.

[Explanation of symbols]

 Reference Signs List 1 laser light 101 laser 102 stabilizer 103 modulator 104 optical head 105 glass substrate 106 format signal source

Claims (7)

[Claims] 1. An optical disc master manufacturing apparatus for forming a pattern for forming pits using an exposure process using a laser beam as a light source, comprising: a clock signal generating means for generating a clock signal at a constant cycle T; Pulse light generating means for generating a laser pulse light whose exposure time is nT times an integer (n) times T, and an intensity P of the laser pulse light whose time is nT as the exposure time
An optical disc master manufacturing apparatus, comprising: a light intensity correcting means for correcting (nT) by the following equation. P (nT) = a · n ^−b × P (min) 1.1 ≦ a ≦ 1.4 0.15 ≦ b ≦ 0.30 P (min): laser intensity at the time of forming the shortest pit pattern 2. The method according to claim 1, wherein the laser light is spot light having a circular cross section with a diameter d, and the pulse light is one of d.
When forming the 0-fold or more the length of the pit pattern, claim 1, further comprising an exposure time correction means for correcting the exposure time nT of the laser pulse light, the exposure time nT _c by the following equation 3. An optical disc master production apparatus according to claim 1. nT _c = (n + a) T 1.0 ≦ a ≦ 2.0 3. A method for manufacturing a master optical disc for forming a pit pattern for pit formation using an exposure process using a laser beam as a light source, wherein a time nT that is an integer (n) times the period T of a clock signal is set to an exposure time A pulse light generating step of generating a laser pulse light, and a light intensity correcting step of correcting the intensity P (nT) of the laser pulse light generated using the time nT as an exposure time by the following equation. A method for manufacturing a master optical disc, comprising: P (nT) = a · n ^−b × P (min) 1.1 ≦ a ≦ 1.4 0.15 ≦ b ≦ 0.30 P (min): laser intensity at the time of forming the shortest pit pattern 4. The laser light is a spot light having a circular cross section with a diameter d, and the pulse light generated in the pulse light generating step forms a pit pattern having a length of 10 times or more of d. If you, optical disk master manufacturing method according to claim 3, further comprising an exposure time correction step of correcting the exposure time nT of the laser pulse light, the exposure time nT _c by the following equation. nT _c = (n + a) T 1.0 ≦ a ≦ 2.0 5. An optical disk constituted by using a substrate on which a pit row is formed, wherein a width W1 of a shortest pit having the shortest length among pits included in the pit row, and a longest pit having a longest length An optical disc, wherein the width W2 of the longest pit is in a relationship of W1 / W2 = 0.8 to 1.2. 6. A width W of a pit included in the pit row
6. The optical disk according to claim 5, wherein a relationship between the track pitch and the track pitch Tp in the pit row is 0.3 Tp.ltoreq.W.ltoreq.0.7 Tp. 7. The length P of a pit included in the pit row
7. The optical disk according to claim 5, wherein l and a space length Ps between pits in the pit row have a relationship of Pl / (Pl + Ps) = 0.4 to 0.6.