JP3448661B2 - Synthetic quartz type for optical disk and optical disk - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz mold for an optical disc and an optical disc.

[0002]

2. Description of the Related Art Optical recording media capable of storing information at high density are expected to become widespread as large-capacity external memories. Among them, optical disks can be reproduced at high speed. It is attracting attention as an external memory for computers. Various types of optical recording media with different information storage methods and sizes have been proposed. Among them, the write-once type and the rewriting of information in which the information can be written only once with the size of 5.25 inches in diameter are proposed. Possible magneto-optical types, ROM type that is read-only for 3.5-inch diameter, magneto-optical type, and partial ROM type that mixes magneto-optical and ROM are standardized by ISO standard. It is expected to become even more widely marketed.

Recently, optical discs have begun to be applied in the digital audio field. For example,
A player using a write-once type optical disk or a magneto-optical disk has been put on the market as a master source in 24-48 digital multi-track recording. In addition to such products for professionals, CD-Rs (light once type compact discs) and MDs (mini discs) have also appeared in products for general consumers, and future trends are drawing attention.

On these optical disks, guides for orderly arranging the information marks by the laser beam from the optical pickup of the recording / reproducing apparatus, that is, for tracking are formed in the form of concave or convex grooves from the inner circumference of the disk. It is formed in a spiral shape toward the outer circumference. This groove is called a guide groove. If the guide groove is further described in detail, as defined in the ISO standard,
A portion that is concave when viewed from the optical pickup, that is, a portion that is distant is called a land, and a portion that is convex when viewed from the pickup, that is, a portion that is near is called a groove. Information is recorded on either lands or grooves. Recording on a land is called a land recording method, and recording on a groove is called a groove recording method. A route for recording information is called a track. From the center of the track to the center of the next track,
We call it track pitch.

Since mass production of the same shape is required for mass production of optical disks, a molding die having a shape in which guide grooves (grooves = grooves), ROM information, preformat information and the like are inverted is formed on the surface. It is common to use the type called. A conventional method of manufacturing a mold for an optical disc will be described with reference to FIG. First, the surface roughness (Ra) 1
Precisely cleaned blue sheet glass master that was precision polished to less than nm
(1) After that, a primer such as a silane coupling agent is applied to the surface, and then a resist is applied (2). Then Ar
The resist is exposed by laser light, He-Cd laser light, Kr laser light, ultraviolet rays, deep ultraviolet rays, etc. according to a predetermined pattern such as guide grooves, ROM information, preformat information (3), and then a developing solution such as inorganic alkali. Development is carried out using to form a predetermined resist pattern on the master surface (4). Next, the surface of the resist pattern is made conductive by sputtering a Ni film (5), and further Ni electroforming is performed.
(6). Then, after polishing the Ni electroformed surface,
The Ni layer is peeled off (7), ashing is performed in plasma to remove the residual resist adhering to the surface of the glass master, and the stamper is completed (8).

Then, (a) an optical disk substrate is manufactured by directly transferring irregularities of a predetermined pattern onto a plastic substrate by an injection molding method using this stamper, or (b) an ultraviolet curable resin liquid on the stamper. And a glass substrate is placed on the glass substrate, and the resin liquid is cured by irradiating ultraviolet rays through the glass substrate, and the unevenness of a predetermined pattern is transferred to the resin layer. An optical disk substrate called a 2P substrate made of members is manufactured. The latter (b) method is 2P
Called the law. A recording film such as a write-once recording layer, a phase change recording layer, and a magneto-optical recording layer is formed on these optical disk substrates, and a protective film is formed and a protective substrate is adhered to manufacture an optical disk. In this specification, for convenience of description, the term “optical disk” may mean an optical disk substrate. By the way, various methods for further increasing the recording density on an optical disc have been proposed. For example, narrowing the track pitch is intended to increase the recording density by making the track pitch, which was conventionally 1.6 μm pitch, smaller. A land and groove recording method has been proposed as another method. In contrast to recording data on either land or groove in the past,
This is a method for recording on both the land and the groove to double the recording capacity (a method for recording on both the land and the groove). In the case of this method, since the data written in the land and the data written in the groove are read at a high C / N ratio, it is common to make the land width and the groove width substantially equal. In other words, track pitch 1.6
In the case of μm, both the land width and the groove width are 0.8 μm.

[0007]

However, when a conventional optical disk manufacturing method is used to manufacture an optical disk with a narrow track pitch as described above or an optical disk of the "system for recording on both lands and grooves", a reproduction signal is reproduced. It was found that a high C / N ratio cannot be obtained and a data reading error is likely to occur due to a high noise level.

According to the discovery of the present inventor, this occurs because the surface of the groove side wall, which is the boundary between the land and the groove, becomes rough due to variations in the sensitivity of the resist.
That is, the reproduction light spot is scattered by the roughness of the side wall surface and the amount of reflected light varies, so that the noise component in the data signal of the optical disk becomes large. In order to reduce this noise level, it is expected that the resist material will be changed to one that is less likely to cause sensitivity variations, but a high-sensitivity material that does not roughen the sidewall surface will also improve the dissolution characteristics in the developer. As a result, the residual film rate of the unexposed portion is reduced, and as a result, the portion where the resist remains, that is, the groove (Note: the front side is the land when viewed from the substrate side, the rear side is the groove), the surface is rough, There is a problem that the noise level of the groove becomes high.

Therefore, a dry etching method has been attempted in which a master is formed with a resist pattern (such as glass or quartz) by reactive ion etching to etch a predetermined pattern on the master to manufacture a stamper. In this case, the residual resist remaining on the surface of the master after etching is removed with a remover. However, even with this method, the roughness of the side wall surface of the groove is not significantly reduced. Also, when a predetermined pattern is etched and the master is used as it is as a mold, when the optical disk substrate is duplicated by the injection molding method or the 2P method, the releasability is poor, and therefore the number of duplicated sheets is several hundred to several thousand. , The land / groove pattern of the mold is broken, and the durability of the mold is poor.

[0010]

As a result of earnest research for solving the above problems, the present inventor has used synthetic quartz as a master material and used CHF as a gas in reactive ion etching.
_{3. With} a gas pressure of less than 0.5 Pa and a self-bias voltage of 500 V or less between the electrodes in the reactive ion etching system, the "groove side wall surface roughness (Ra) was the first to invent a synthetic quartz mold having a thickness of 1 nm or less (first invention). When this quartz mold is used as it is as a mold, a quartz mold with improved durability is obtained, and a plastic optical disk molded with this quartz mold has a reduced noise level and a high C / N ratio. It has been found.

The present invention has a plurality of types and is not limited to this synthetic quartz mold for optical disks (first invention), and several inventions will be described below.

[0012]

Roughness does not occur on the side wall surface of the groove etched in the master, that is, the side wall surface roughness of the groove (R
In order to reduce a), the present inventor has selected synthetic quartz as a material for the master and found special conditions of reactive ion etching for processing it (etching grooves). Synthetic quartz has very few impurities and almost 100%
Since it is SiO ₂ , the roughness of the etched surface (etching bottom surface = see FIG. 6), that is, the bottom surface of the groove and the side wall surface can be extremely reduced. The degree of roughness is represented by surface roughness (Ra).

When processing synthetic quartz by reactive ion etching into a quartz mold, the conventional conditions were that the gas was CF ₄ , the gas pressure was 0.5 Pa or higher, and the self-bias voltage was 600 V or higher. However, the quartz mold manufactured under these conditions has a problem that the roughness of the bottom surface of the groove is small, but the roughness of the side wall of the groove is large.

In order to reduce the roughness of the side wall surface, the inventor of the present invention has a ratio of the etching rate of the resist functioning as a mask material to the synthetic quartz to be etched, that is, "the etching rate of synthetic quartz / the etching rate of the resist". By setting the reactive ion etching condition with a large selection ratio, the rate of roughening the side wall of the mask material is reduced. We found that it can be smoothed.

Further, the present inventor has found that one of the causes of the poor mold releasability of the quartz mold manufactured by the dry etching method is the roughness of the side wall surface. It was also found that the moldability was improved at the same time and the number of copies could be increased. It was also found that CHF ₃ is more suitable than CF _{4 as} a gas, a lower gas pressure is better, and a lower self-bias voltage improves the selection ratio. The relationship between the self-bias voltage and the selection ratio is shown in FIG. 2, and the relationship between the gas pressure and the selection ratio is shown in FIG. Further, the relationship between the selectivity and the side wall surface roughness is shown in FIG. As a result of measuring the noise level of the quartz type, the gas pressure is preferably less than 0.5 Pa, more preferably less than 0.3 Pa, and the self-bias voltage is preferably 500 V or less, more preferably 300 V or less.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0017]

Example: First, the outer diameter is 350 mm, the inner diameter is 70 mm, and the thickness is 6 m.
A synthetic quartz master, which was polished to a surface roughness of 1 nm or less at m, was immersed for 5 minutes in a liquid (concentration: 40 ° C) in which concentrated sulfuric acid and hydrogen peroxide solution were mixed at a volume ratio of 4: 1. After that, ultrapure water,
Ultrasonic cleaning was sequentially performed with a CFC organic solvent (Asahi Klin AK225AES manufactured by Asahi Glass) (1).

Next, after spin coating a primer (anchor coat manufactured by Transyl Co.) on the surface of the synthetic quartz master,
A positive resist (AZ1350 manufactured by Hoechst) was spin-coated. Then, the master was prebaked for 30 minutes in a clean oven at 100 ° C. By the way, the resist film thickness is about
220 nm (2). Next, an area from the radius of 72 mm to the radius of 148 mm of the master was exposed by a cutting machine using an Ar ion laser with a wavelength of 457.9 nm as a light source.
(3). The track pitch was 1.6 μm, and the laser beam intensity was set so that the land (or groove) width was formed to be about 0.8 μm after development, and continuous exposure was performed. The rotation speed of the synthetic quartz master during exposure is 450 rpm, and the laser beam spot diameter is about 1.3 μm.

Thereafter, the volume ratio of the inorganic alkaline developer (trade name "AZ Developer" manufactured by Hoechst) and ultrapure water was 3: 3.
Spin-developed with a diluted developer mixed at a ratio of 5 (4)
. At this time, the developing conditions are the pure water application time as pretreatment.
Seconds, the developer coating time was 98 seconds, the pure water shower time as the post-treatment was 90 seconds, and the spin drying time was 90 seconds. Then, it was post-baked in a clean oven at 120 ° C. for 30 minutes.

After that, the master was placed in the chamber of a reactive ion etching apparatus (DEA506 manufactured by Nichiden Anelva), and after evacuating to a vacuum degree of 1 × 10 ^-4 Pa, CHF ₃ gas was introduced to carry out reactive ion etching. (Five) . At this time, the gas flow rate is 6 sccm, the gas pressure is 0.3 Pa, and the RF power is
300W, self-bias voltage is 300V, distance between electrodes is 100m
m, the etching time was 9 minutes. The groove depth at this time was about 85 nm.

Next, concentrated sulfuric acid and hydrogen peroxide solution were mixed in a volume ratio of 4:
The master was dipped in a liquid mixed at a ratio of 1 and the residual resist was peeled off to obtain a quartz mold (6). The liquid temperature at this time was 100 ° C., and the treatment time was 5 minutes. After that, ultrapure water, CFC-based organic solvent (trade name “Asahi Klin” manufactured by Asahi Glass Co., Ltd.)
The quartz mold was finished by ultrasonic cleaning with AK225AES). This quartz mold is provided with a groove and a land, and the surface roughness (Ra) of the groove side wall and the surface roughness (Ra) of the land are both 1 n.
It was m or less. Thereafter, using this quartz mold, a 2P method for an optical disk having a resin layer in which a predetermined pattern (land / groove pattern) having a groove sidewall roughness of 1 nm or less is duplicated on the surface of a glass substrate having a diameter of 304.8 mm. The substrate was manufactured.

Next, the silicon nitride (S
i3N4) dielectric layer, TbFeCo magneto-optical recording layer, silicon nitride (S
After forming the i3N4) protective layer in this order, a protective substrate was adhered to the film surface with an ultraviolet curable adhesive to manufacture a magneto-optical disk. This optical disc is reproduced by a pickup that has a wavelength of 830 nm, an NA of 0.55, a vignetting coefficient of 1.0, a wavefront aberration of 0.03 λ (rms value), a linearly polarized light, and its direction is parallel to the guide groove. The light intensity signal output was input to a spectrum analyzer and the noise level of the land and groove was measured. The reproduction beam intensity at this time is 1.0 mW, the rotation speed is 1800 rpm, and the radial position is 75 mm.
Met. Table 1 shows the measurement results of the land noise level.
Table 2 shows the measurement results of the noise level of the groove. The noise level of the land and the noise level of the groove were both good, and could be clearly lower than the noise level of the optical disc manufactured by the conventional stamper.

Further, the quartz mold of Example 1 is repeatedly used,
Even after copying 200,000 optical disk substrates by the 2P method,
No damage occurred to the land / groove pattern of the mold. In addition, the stamper may be duplicated from the quartz mold of Example 1 according to a known technique (Japanese Patent Laid-Open No. 5-205321, etc.).

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As described above, the present invention can reduce the surface roughness (Ra) of the boundary between the groove and the land (groove side wall) and the bottom surface of the groove. It is possible to provide a noise level optical disc and a quartz mold having high durability.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram illustrating a quartz mold manufacturing method according to a first embodiment.

FIG. 2 is a diagram showing a correlation between a selection ratio and a self-bias voltage.

FIG. 3 is a diagram showing a correlation between a surface roughness (Ra) of a sidewall and a selection ratio.

FIG. 4 is a diagram showing a correlation between gas pressure and selection ratio.

FIG. 5 is a manufacturing process diagram showing a conventional quartz mold manufacturing method.

FIG. 6 is a view showing a side wall surface of a quartz mold.

[Explanation of symbols]

1 ... Master made of synthetic quartz 2 ... Resist 3 ... Picking up of cutting machine 4 ... Exposed part 5: Unexposed part 6 ... Master made of blue plate glass 7: Ni sputtered film 8: Ni plating layer 9 ... residual resist

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-4-241237 (JP, A)                 JP-A-60-147946 (JP, A)                 JP-A 1-205744 (JP, A)                 JP-A-61-240452 (JP, A)                 JP-A-6-349115 (JP, A)                 JP 61-123035 (JP, A)                 Japanese Patent Laid-Open No. 5-258344 (JP, A)                 JP-A-7-29186 (JP, A)                 Japanese Patent Laid-Open No. 5-282713 (JP, A)                 JP-A-4-307441 (JP, A)                 JP 63-50938 (JP, A)

Claims (7)

(57) [Claims] 1. A quartz mold for an optical disk having a groove and a land, wherein a sidewall surface roughness (Ra) of the groove is provided.
Is a synthetic quartz mold for optical discs of 1 nm or less. 2. The surface roughness (Ra) of the land is 1 nm.
The synthetic quartz mold according to claim 1, wherein: 3. The synthetic quartz mold according to claim 1, wherein the land width and the groove width are both 0.8 μm or less. 4. The synthetic quartz mold according to claim 1, wherein the quartz mold is for an optical disk of a type in which recording is performed on both the land and the groove. 5. A plastic optical disk molded by using the synthetic quartz mold according to claim 1. 6. A groove has a sidewall surface roughness (Ra) of 1 n.
An optical disc of m or less. 7. The groove has a sidewall surface roughness (Ra) of 1 n.
An optical disc that can be recorded on both lands and grooves below m.