JP2002092984A - Stamper, producing method thereof and plastic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the variation of recording/reproducing output due to fine ruggedness existing on a plastic substrate used in a film surface incidence type optical recording medium. SOLUTION: In this stamper which is made by electroplating method and is used for injection molding of the plastic substrate for optical disk, the center line average roughness Ra of stamper back surface after the completion of electroplating is less than 1.5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic substrate for an optical disk manufactured by using a stamper and a stamper used for injection molding of the plastic substrate for an optical disk.

[0002]

2. Description of the Related Art With the advent of the multimedia age, optical recording media have been widely used as media capable of recording and reproducing a large amount of information such as music, moving images, and computer data. Optical recording media include read-only optical recording media that can only read information, such as CDs and laser disks (registered trademark), and write-once optical recording media, which can record only once, such as CD-Rs. However, it is classified as a rewritable optical recording medium on which data can be rewritten and erased.

In recent years, as the amount of information to be handled has increased, it has been demanded that the recording capacity of an optical recording medium be further increased. As a means for responding to this demand, there has been proposed a method of performing recording and reproduction using a flying head equipped with a solid immersion lens (SIL). According to this method, recording and reproduction can be performed with a smaller light spot diameter than in the related art, so that the recording density per unit area can be increased by about one digit as compared with the conventional magneto-optical recording medium.

When recording and reproducing using SIL, near-field light oozing from SIL can be used as recording and reproducing light. Since the near-field light is attenuated at a distance of about 光 of the wavelength of the light, the distance between the SIL and the recording layer needs to be 1 or less of the wavelength of the recording / reproducing light. For this reason, when near-field light is used, a method is adopted in which laser light is incident from the thin film lamination surface opposite to the substrate. Since the laser beam is incident from the thin layer lamination surface, the lamination order of the magneto-optical recording medium using near-field light is also different from that of the conventional medium, and usually, a reflective layer, a heat diffusion layer, a recording layer, It has a structure in which body layers are sequentially laminated. In order to increase the recording density by narrowing the spot of the laser beam to a smaller size, a lens with a high NA is used. When using a high NA lens, the tilt of the substrate
Coma and astigmatism due to (tilt) increase. Since coma and astigmatism are proportional to the thickness of the substrate, when using a lens with a high NA, to reduce these aberrations, the thickness of the substrate to be used should be reduced, or as in near-field recording. Recording and reproduction are performed by irradiating a laser beam from the film surface. In the film surface incidence method, since the thickness of the substrate is almost zero, the coma aberration and the astigmatism due to the inclination of the substrate are suppressed. Therefore, film-surface incident type optical recording including near-field recording can be said to be a recording method suitable for high-density optical recording in the future.

As described above, the film surface incidence method including near-field recording is a recording method suitable for high-density optical recording. However, in this method, the distance between the optical head and the disk surface is higher than that of a conventional optical disk. However, there is a problem that the recording / reproducing output fluctuates.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to reduce minute unevenness present on a plastic substrate used in a film surface incidence type optical recording system. More specifically, the present invention relates to a stamper for producing such a plastic substrate.

[0007]

First, fine irregularities existing on a plastic substrate are defined. United States KLATen
Using a cork DISK PROFILER TENCOR-P12, with a stylus made of diamond and having a radius of curvature of 2 μm, load 5m
g, a scanning speed of 400 μm / s and a scanning width of 20 mm are used to measure minute undulations present on the plastic substrate. Under these measurement conditions, minute undulations having a wavelength of 45 μm to 4.5 mm are extracted within a scanning width of 20 mm, and the maximum amplitude of these undulations is defined as minute unevenness existing on the plastic substrate.

According to the present invention, by setting the center line average roughness Ra of the back surface of the stamper manufactured by the electrolytic plating method to less than 1.5 μm, it is possible to reduce minute unevenness existing on the plastic substrate.

It is considered that the fine irregularities existing on the injection-molded plastic substrate are formed by the following mechanism. After plating, the back surface of the stamper is usually polished by a polishing apparatus. However, if the center line average roughness Ra of the stamper back surface after plating is larger than 1.5 μm,
Sufficient smoothness cannot be obtained even by polishing the back surface of the stamper. When a plastic substrate is injection-molded using such a stamper, the high surface pressure of the back surface elastically propagates the signal surface due to the high pressure during molding, and minute irregularities are transferred to the plastic substrate. It is considered that there are minute irregularities existing on the upper side. Therefore, in order to reduce minute unevenness existing on the plastic substrate,
It is necessary to suppress the surface roughness of the stamper back surface after plating to less than a certain value. As a result of intensive studies by the inventor,
The center line average roughness Ra of the stamper back surface after plating is 1.5
By suppressing the diameter to less than μm, it has been found that minute unevenness existing on the injection-molded plastic substrate can be reduced to less than 35 nm _pp . On the back of the stamper after plating is completed
Ra is more preferably less than 0.5 μm. In this case, fine irregularities existing on the plastic substrate can be suppressed to 25 nm _pp or less.

In order to keep the center line average roughness Ra of the rear surface of the stamper after plating to less than 1.5 μm, the current density during stamper plating needs to be 7.5 A / dm ² or less. A nickel sulfamate bath is usually used for plating the stamper. Nickel sulfamate bath 1,3,6 naphthalene tris sulfone sodium, saccharin, p- toluenesulfonic acid, and without the addition of brightener such as benzenesulfonic acid, plating a stamper in the following current density 7.5A / dm ² Then, the crystal grains grow in a direction perpendicular to the film surface. Therefore, the center line average roughness of the stamper back surface after plating is completed
Ra is considered to be suppressed to less than 1.5 μm. When a brightener such as sodium 1,3,6-naphthalene trisulfonate, saccharin, p-toluenesulfonic acid and benzenesulfonic acid is added to the nickel sulfamate bath, the stamper has a current density of 7.5 A / dm ² or less. It is considered that when plating is performed, the crystal grains of the stamper material are refined, and as a result, the center line average roughness Ra of the back surface of the stamper is suppressed to less than 1.5 μm.

When a brightener is added to the plating bath, the brightener molecules are adsorbed to crystal growth points, and have an effect of suppressing the crystal growth. Therefore, when plating is performed by adding a brightening agent to the plating bath, the crystal grains become finer and the roughness of the back surface of the stamper can be suppressed.

When a plastic substrate is injection-molded using a stamper plated under the above conditions, the fine irregularities existing on the plastic substrate can be suppressed to less than 35 nm _pp .
The electroplating is preferably performed at a current density of 5 A / dm ² or less. If the current density of 5A / dm ² below, the center line average roughness Ra of the stamper backside becomes 0.5μm or less, fine irregularities present in the injection molded plastic substrate using this stamper kept below 25 nm _pp Can be

On the other hand, the current density during stamper plating is 7.5 A
When greater than / dm ^2, 1 to nickel sulfamate bath,
3,6-naphthalene sodium trisulfonate, saccharin,
When a brightener such as p-toluenesulfonic acid or benzenesulfonic acid is not added, the crystal grains of the stamper material become dendritic, and the crystal grains grow throughout the film. As a result, Ra on the back surface of the stamper has a large value of 1.5 μm or more. Further, 1,3,6-naphthalene tris sulfone sodium nickel sulfamate bath, saccharin, p- toluenesulfonic acid and the case of adding gloss agent such as benzenesulfonic acid, higher current density than 7.5A / dm ² stampers When plating with, the crystal grains become coarse, and as a result
Ra is a large value of 1.5 μm or more. When a plastic substrate is injection molded using a stamper plated under these conditions, the fine irregularities on the plastic substrate are 35 nm
_{It is} a large value of _pp or more.

As described above, when a plastic substrate is injection-molded with a stamper having a current density of 7.5 A / dm ² or less and a center line average roughness Ra of the rear surface thereof is less than 1.5 μm, the plastic substrate is formed on the plastic substrate. 35 nm for existing minute irregularities
It can be suppressed to less than _pp . However, generally 7.5A / dm
^{When a} stamper is plated at a low current density of ² or less, a compressive stress is generated in the stamper. If the compressive stress is large, it causes a problem that the stamper cannot be mounted on the mold of the molding machine. For this reason, actually 90% to 9% of the total thickness of the stamper
5% were plated at a low current density of 7.5A / dm ² or less, 7.5A the remainder
Plating at a high current density greater than / dm ² is preferred.
Doing plated at 7.5A / dm ² larger high current densities, since it is able to generate a tensile stress on the stamper, 7.5A
With a low current density of / dm ² or less, the compressive stress generated by plating can be canceled. At this time, the center line average roughness Ra of the stamper backside by increasing the current density increases, since the plating of 90-95% of the stamper at a low current density of 7.5A / dm ² or less, the final stamper The center line average roughness Ra of the back surface can be reduced to less than 1.5 μm.

As a material for electrolytic plating of the stamper,
Materials such as Ni, NiCo, NiP, NiB, and CoAg can be mentioned, and among them, Ni is more preferably used.

An example in which Ni is used as a stamper material will be described below. In order to electroplate Ni on the glass master,
A conductive thin film is formed on a glass master. Generally, 30 to 100 nm by sputtering or electroless Ni plating.
Ni or NiP thin films are provided on a glass master. Since the thickness of these conductive thin films is as thin as 30 to 100 nm, when the current density is increased in a short time of less than 10 minutes, the generated Joule heat causes the film to be cut, so that electrolytic plating cannot be performed. Therefore, the current density during Ni plating was increased to 7.5 A / d over 10 minutes.
The current density is increased to a predetermined current density of m ² or less. More preferably
The current is increased to a predetermined current density of 7.5 A / dm ² or less over 35 minutes or more. According to this method, Ni of several microns grows on the conductive Ni or NiP thin film, so that even after the current is increased to a predetermined current density of 7.5 A / dm ² or less, the film does not break and stable electrolytic plating is performed. I can do it.

As a plating bath for the stamper, a nickel sulfamate bath is usually used. The nickel sulfamate bath is composed of nickel sulfamate, nickel chloride and boric acid, and may optionally contain brighteners such as 1,3,6-naphthalene sodium trisulfonate, saccharin, p-toluenesulfonic acid and benzenesulfonic acid. You may.
The addition concentration is, for example, about 1/2500 with respect to the total Ni concentration.

[0018]

Embodiments of the present invention will be specifically described below.

Example 1 Direct electroless Ni plating
70nm as a conductive film on a glass master with a diameter of 200mm and thickness of 6mm
A NiP thin film was provided. Then, using a sulfamic acid bath,
According to the current density profile below, a 300 μm thick
The electrodes were electroplated. 2.5 A / dm current density ^TwoUntil 35 minutes
And then increase the current density to 2.5 A / dm^TwoWith a thickness of 275μm
22.3 A / dm^TwoHigh current density
Plated.

(Example 2) A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Thereafter, using a sulfamic acid bath, a stamper having a thickness of 300 μm was electroplated according to the following current density profile. The current density was increased to 5 A / dm ² over 35 minutes, then plated at a current density of 5 A / dm ² to a thickness of 275 μm and the remaining 25 μm plated at a high current density of 22.3 A / dm ² .

(Embodiment 3) Direct electroless Ni plating
70nm as a conductive film on a glass master with a diameter of 200mm and thickness of 6mm
A NiP thin film was provided. Then, using a sulfamic acid bath,
According to the current density profile below, a 300 μm thick
The electrodes were electroplated. 7.5 A / dm current density ^TwoUntil 35 minutes
And then raise the current density to 7.5 A / dm^TwoAt 275μm thickness
Until the remaining 25μm is 22.3 A / dm^TwoWith high current density
Plated.

Example 4 A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Then, using a sulfamic acid bath, sodium 1,3,6-naphthalene trisulfonate was used as a brightener.
Ni was added at a concentration of 7.3 × 10 ⁻⁴ mol / L to a total concentration of 1.9 mol / L, and a stamper having a thickness of 300 μm was electroplated according to the following current density profile. The current density up to 5 A / dm ² 35
It was then raised over a minute and then plated at a current density of 5 A / dm ² to a thickness of 275 μm and the remaining 25 μm plated at a high current density of 22.3 A / dm ² .

Example 5 A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Then, using a sulfamic acid bath, sodium 1,3,6-naphthalene trisulfonate was used as a brightener.
Ni was added at a concentration of 7.3 × 10 ⁻⁴ mol / L to a total concentration of 1.9 mol / L, and a stamper having a thickness of 300 μm was electroplated according to the following current density profile. Current density up to 7.5 A / dm ² 3
Raised over 5 minutes, then plated at a current density of 7.5 A / dm ² to a thickness of 275 μm and the remaining 25 μm plated at a high current density of 22.3 A / dm ² .

Comparative Example 1 A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Thereafter, using a sulfamic acid bath, a stamper having a thickness of 300 μm was electroplated according to the following current density profile. The current density was increased to 10 A / dm ² over 35 minutes and then plated to 300 μm at a current density of 10 A / dm ² .

(Comparative Example 2) A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Thereafter, using a sulfamic acid bath, a stamper having a thickness of 300 μm was electroplated according to the following current density profile. The current density was increased to 15 A / dm ² over 35 minutes and then plated to 300 μm at a current density of 15 A / dm ² .

(Comparative Example 3) A 70 nm thick conductive film was formed on a glass master having a diameter of 200 mm and a thickness of 6 mm by electroless Ni plating.
A NiP thin film was provided. Thereafter, using a sulfamic acid bath, a stamper having a thickness of 300 μm was electroplated according to the following current density profile. The current density was raised to 22.3 A / dm ² over 35 minutes and then plated to a current density of 22.3 A / dm ² to 300 μm.

The center line average roughness Ra of the back surface of each of the stampers obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was measured using a contact type surface roughness meter SJ-201 manufactured by Mitutoyo. The stylus was a diamond with a radius of curvature of 2 μm at the tip and measured at four points at a stamper radius of 60 to 65 mm. Then, Examples 1 to 5 and Comparative Examples 1 to
The stamper plated in Step 3 was polished on the back surface without peeling from the glass master, and then the stamper was peeled from the glass master and punched into a predetermined size. These stampers were loaded into a mold of an injection molding machine, and a polycarbonate substrate was produced by injection molding a polycarbonate resin material into the mold. KLA Tencor's DISK PROFILER TENCOR-P of the U.S.A.
It measured using 12. The results are summarized in Table 1.

[0028]

[Table 1]

As is clear from the table, the stamper was set to 7.5 A / dm ²
When plating with the following current density, Ra on the back of the stamper is
The value is less than 1.5 μm, and the fine unevenness existing on the plastic substrate molded using these stampers is 35 nm.
less than _pp . Also, when the plated stamper at a current density of 5A / dm ^2, Ra of the stamper backside becomes a value of less than 0.5 [mu] m, fine irregularities present on the molded plastic substrate using these stampers less than 25 nm _pp Can be suppressed. If a plastic substrate is injection-molded using the stamper of the embodiment, minute irregularities existing on the plastic substrate can be suppressed to less than 35 nm _pp , and as a result, output fluctuation during recording / reproduction can be minimized.

Although the present invention has been described in detail, the stamper according to the present invention is not limited to a magneto-optical recording medium, but may be a phase-change optical recording medium or a write-once optical recording medium having an organic dye in a recording layer. The present invention can be applied to any optical recording medium such as a medium and a read-only optical recording medium.

[0031]

According to the stamper of the present invention, the current density during stamper plating can be set to 7.5 A / dm ² or less, and the center line average roughness Ra of the stamper rear surface after plating can be set to less than 1.5 μm. As a result, it is possible to reduce the fine irregularities existing on the plastic substrate injection-molded using the stamper of the present invention to less than 35 nm _pp, and to suppress the output fluctuation during recording and reproduction.

Claims (5)

[Claims] 1. A stamper manufactured by electrolytic plating and used for injection molding of a plastic substrate for an optical disk, characterized in that the center line average roughness Ra of the back surface of the stamper after the completion of electrolytic plating is less than 1.5 μm. Stamper. 2. The stamper according to claim 1, wherein the material of the stamper is Ni. 3. A method for producing a stamper manufactured by an electrolytic plating method and having a center line average roughness Ra of less than 1.5 μm on the back surface of the stamper after the completion of the electrolytic plating. A method for manufacturing a stamper, wherein the density is 7.5 A / dm ² or less. 4. The method of manufacturing a stamper according to claim 3, wherein the current density during electrolytic plating is 7.5 A / d over 10 minutes or more.
m ² raised to the following predetermined current density, 90% to 95% of the rear 7.5A / dm ² or less for a given current density in all the stamper thickness and electroplating, after which the remainder of the stamper 7.5A / dm ² A method for manufacturing a stamper, wherein plating is performed at a higher current density. 5. A plastic substrate injection-molded by using the stamper according to claim 1, wherein minute irregularities present on the surface of the plastic are less than 35 nm _pp .