JP2004079118A - Stamper, its manufacturing method, and optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stamper capable of reducing defects due to releasing failure in a molding process and improving the signal characteristics of an obtained optical disk. <P>SOLUTION: For a 3T pit and a longer pit of 8T or more, respective widths are defined as W<SB>3T</SB>and W<SB>L</SB>, pit heights as H<SB>3T</SB>and T<SB>L</SB>, the inclination angles of the pit side walls in the radial direction as AR<SB>3T</SB>and AR<SB>L</SB>and the inclination angles of the pit side walls in the tangential direction as AT<SB>3T</SB>and AT<SB>L</SB>. Then the pit of the 3T pit shape satisfies inequalities 200 nm≤W<SB>3T</SB>≤270 nm, 120 nm≤H<SB>3T</SB>≤160 nm, 40 degrees≤AR<SB>3T</SB>≤55 degrees, and 30 degrees≤AT<SB>3T</SB>≤50 degrees, and the pit shape of the longer pit satisfies inequalities 200 nm≤W<SB>L</SB>≤280 nm, 120 nm≤H<SB>L</SB>≤160 nm, 40 degrees≤AR<SB>L</SB>≤55 degrees, 30 degrees≤AT<SB>L</SB>≤55 degrees and ¾W<SB>L</SB>-W<SB>3T</SB>¾≤30 nm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stamper for manufacturing an optical disk such as a DVD, a method for manufacturing the same, and an optical disk manufactured using the stamper.
[0002]
[Prior art]
The information on the optical disk is recorded as a fine concave-convex pattern on the reflection surface, which is detected by the read head of the reproducing device as the intensity of the reflected light, and converted into useful information. With the spread of personal computers in recent years, this optical disk is widely used as an information medium in addition to music and images. In particular, since it can be mass-produced by injection molding in addition to the convenience at the time of use, it is possible to provide information at a low price, and the production volume is expected to increase further in the future.
[0003]
A stamper, which is a mold for injection molding an optical disc, has pits or grooves in the state of the optical disc (although, in the present specification, they are also called pits). The pit pattern is projected and transferred to a resin disk by injection molding to produce an optical disk.
[0004]
The stamper used for manufacturing this optical disk is a nickel disk having a thickness of about 0.3 mm, and the number of optical disks made from one stamper is at most about tens of thousands. Also, stampers of a type corresponding to the number of information contents must be manufactured. Therefore, it is considered that the number of stampers consumed will increase more and more in the future.
[0005]
Since such stampers require strict quality in terms of pit shapes, surface defects, mechanical strains, and the like, the stampers are currently manufactured by the following production process using microfabrication technology.
[0006]
First, a resist layer of a predetermined thickness is formed on the surface of a precision-polished disk-shaped glass plate by spin coating, the solvent is removed by baking, and then the resist layer is exposed to a laser beam by a laser exposure device. Let it. At this time, the intensity of the exposure beam is modulated by the signal source, and is written on the resist layer as information of the signal source.
[0007]
Thereafter, the exposed portion of the resist layer is removed in a developing step, and information is formed as a pit pattern on the resist surface. Next, after conducting a surface conductive treatment by applying a metal film by sputtering, plating, or the like, the film is thickened to a nickel plate of about 0.3 mm by nickel electrolytic plating. The nickel plate thickened by plating is peeled off from the glass substrate and becomes a stamper after cleaning the front surface, polishing the back surface, and processing the inner and outer diameters to a specified size.
[0008]
After the stamper is manufactured by the above process, it is put into a molding process after signal inspection. In the molding step, an optical disk is manufactured by injection molding using a polycarbonate resin. In other words, molten polycarbonate is injected into the cavity of the mold formed by the stamper set in the mold frame of the injection molding machine, cooled while applying pressure, and the pit pattern on the stamper surface is transferred and peeled off. I do. Therefore, as the performance of the stamper, it is important to have excellent transferability to accurately transfer the pit pattern of the stamper, and to have releasability that does not cause defects and can be peeled off satisfactorily.
[0009]
By the way, optical disks are required to be manufactured at a high yield because the production amount is very large and low-cost production is required. As a cause of the decrease in the yield in the molding process, a defect generated when the optical disk is peeled off from the stamper occupies a relatively large specific gravity. This phenomenon is more remarkable in a stamper of a DVD than in a CD, and at present, the stamper is manufactured by devising to minimize this problem by setting conditions in a manufacturing process and a molding process. For example, the surface treatment of the stamper is performed by plasma ashing, and the temperature is controlled during molding.
[0010]
Transfer defects are less likely to occur in CDs and occur more frequently in DVDs, so it is estimated that the pit shape of the stamper has an effect. However, DVDs use a pit edge recording method. In addition, signal characteristics are likely to be degraded due to a change in shape, and it has been a very difficult task to find pit formation conditions that solve the problems of these molding processes.
[0011]
There are several known documents regarding the shape of the pit. For example, in Japanese Patent Application Laid-Open No. 10-228627, the size of the pits on the outer peripheral portion is set to the inner peripheral portion for the purpose of preventing double transfer and pit misalignment occurring due to mold release failure in a rewritable disc. It is disclosed that the signal amplitude is increased by a maximum of 1.08 times in comparison. Japanese Patent Application Laid-Open No. 9-288852 describes that an inflection surface having a large curvature is set at the corner of the pit top or bottom for the purpose of improving the releasability at the time of molding.
[0012]
[Problems to be solved by the invention]
However, the method disclosed in Japanese Patent Laid-Open No. 10-228627 is a solution for a rewritable disk, and cannot be used when a pit edge recording method such as a DVD is used because the signal quality is deteriorated. Also, the device disclosed in Japanese Patent Application Laid-Open No. 9-288852 cannot be used because the signal rise timing varies and the jitter component increases, so that the signal characteristics are remarkably deteriorated. That is, the methods described in these documents do not consider compatibility between the improvement of the releasability and the DVD signal quality, and a solution to these problems has been an urgent issue for stable production. .
[0013]
In order to manufacture a DVD at a high yield in the production of DVDs, it is necessary to secure good transferability and releasability and also to have good electric signal characteristics. However, conventionally, transfer is performed only by the surface treatment of the stamper as described above. Because the method of improving the moldability and mold releasability was adopted, a reasonable effect could not be obtained, but it was not enough.Also, as a fundamental countermeasure, a method of controlling the shape of the pit was considered. Therefore, it has been considered that it is difficult to achieve both transferability and releasability and electric signal characteristics because the electric signal characteristics cause a decrease in jitter characteristics.
[0014]
That is, if the pit shape is made gentle for the purpose of improving the transferability and the releasability, the jitter characteristics among the signal characteristics of the disk are reduced. Jitter is one of the signal characteristics, and is a standard deviation when a time lag between a read signal and a clock signal is measured, and is specified in the DVD standard. If the inclination of the pit is gentle, the rise and fall of the signal become gentle, and as a result, the fluctuation amount increases and the jitter characteristic deteriorates.
[0015]
Therefore, as a method of improving transferability and releasability after securing signal characteristics, a method of first creating a steep pit and then modifying the surface to improve releasability has been used. Was.
First, pits are formed using a resist having a high γ value. As shown in FIG. 4, the γ value is shown in FIG. 4, where the horizontal axis represents the amount of exposure and the vertical axis represents the residual film ratio of the developed resist, and γ = (log (a / b)) ⁻¹
Is represented by
Here, a is the exposure amount at which the residual film ratio becomes 0%, and b is the exposure amount at which the slope of the characteristic curve is extended and the residual film ratio becomes 100%. If the γ value is higher and the exposure is performed at a certain intensity or higher, only that portion is promptly removed in the developing step, so that a steep pit is formed. In order to obtain high γ characteristics, it is effective to use a UV light source having a shorter wavelength together with selection of a resist. Thereafter, the releasability is improved by surface treatment using plasma or the like. In this method, there are many problems such as the effect of the surface treatment being weakened and the releasability being reduced as the use of the stamper is advanced, and the effect of the surface treatment itself being small, so that the effect may not be exhibited depending on the molding machine. .
[0016]
The present invention has been made in view of the above-mentioned conventional problems, and has provided a stamper, a manufacturing method thereof, and a stamper, in which the effect of improving the moldability is largely exhibited by any molding apparatus, and the moldability of the stamper does not deteriorate even after repeated use. The purpose is to provide.
[0017]
[Means for Solving the Problems]
Stamper of the present invention, the 3T pits and 8T or more long pit, the respective widths _W 3T, _{W L,} the height _H 3T pit, _{H L, AR} 3T an inclination angle in the radial direction of the pit sidewalls, AR _L, and the inclination angle of the tangential direction of the pit sidewalls _AT 3T, as AT _L,
For the 3T pit, 200 nm ≦ W _3T ≦ 270 nm
120 nm ≦ H _3T ≦ 160 nm
40 degrees ≦ AR _3T ≦ 55 degrees 30 degrees ≦ AT _3T ≦ 50 degrees For long pits, 200 nm ≦ W _L ≦ 280 nm
120 nm ≦ _HL ≦ 160 nm
40 ° ≦ A _L ≦ 55 ° 30 ° ≦ AT _L ≦ 55 ° and | W _L −W _3T | ≦ 30 nm
The pit shape satisfies the following conditions.
[0018]
That is, as a result of intensive studies for the purpose of achieving both the signal characteristics of the optical disc and the low defectivity in the molding process, the process conditions for forming the pits of the stamper were appropriately set, and the pit shape of the stamper was adjusted as described above. It has been found that a stamper for a DVD that satisfies both characteristics can be produced by controlling the stamper in the range described above.
[0019]
Note that T is a minimum time unit for signal control during recording / reproduction, and the pit length is defined by a pit length formed by an integral multiple of the T time. The minimum pit length is 3T, and the pit length is 3T to 14T except for 12T and 13T.
[0020]
In addition, when the stamper is manufactured under the process conditions in which the shapes of the 3T pit and the long pit of 8T or more are as described above, the pit shape of 4T to 7T becomes an appropriate shape between them, so it is particularly specified. No need.
[0021]
The above numerical values are average values of the measured values. This is because, since the pit shape is very small, even if pits having the same shape within the above-mentioned proper range are measured, variations in individual measured values exceeding the above-mentioned range cannot be avoided.
[0022]
In addition, when the stamper is made of nickel as a base material, the above-described effects can be ensured in the production of an optical disc because of the mechanical properties required for the stamper, the ease of production by plating, the moldability and mold release properties for polycarbonate resin, and the like. Is preferable.
[0023]
Further, in the stamper manufacturing method of the present invention, the pit pattern having the pit shape is formed on a resist layer formed on the surface of a glass plate, a metal thin film is applied to the surface, and the surface is subjected to a conductive treatment. Is formed, and the nickel plate is peeled off from the glass plate for cleaning. With this manufacturing method, a stamper having the above-described effects can be manufactured.
[0024]
Further, the optical disk of the present invention is manufactured by injection molding using the stamper as a mold, and an optical disk having the above effects can be obtained at low cost.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a stamper of the present invention, a manufacturing process thereof, and a manufacturing process of an optical disk using the stamper will be described with reference to FIGS.
[0026]
First, the manufacturing process of the stamper according to the present embodiment will be described with reference to FIGS. First, as shown in FIG. 2A, a resist layer 12 having a predetermined thickness is applied to a precisely polished and cleaned glass plate 11. The resist layer 12 is formed by coating using a positive resist by spin coating so as to have a constant thickness. The optimum thickness of the resist layer 12 depends on the height of a target pit and a developing step described later, but is generally from 110 nm to 160 nm. Further, in order to improve the adhesion of the resist layer 12 to the glass plate 11 before the resist coating, a solution containing hexamethyldisilazane may be applied to the glass plate, or steam containing the solution may be wiped on the glass plate. Done.
[0027]
The glass plate 11 coated with the resist layer 12 is removed by evaporating a solvent component in the resist layer 12 by baking, and then, as shown in FIG. 3, a laser beam recording device (hereinafter, referred to as LBR) 13. Exposed. The LBR 13 uses a laser 14 as a light source and uses a laser 16 by a modulator 16 such as an EOM (electro-optic modulator) or an AOM (acousto-optic modulator) based on a signal from a DVD signal generator (hereinafter, referred to as a formatter) 15. The beam is intensity-modulated, the beam diameter of the laser beam is expanded by a beam expander 17, then introduced into an objective lens 18, and focused on the surface of the resist layer 12 of the glass plate 11 by the objective lens 18 for exposure. It is. The glass plate 11 is precisely moved in a certain direction while rotating on a turntable 19, and as a result, a spiral recording having a certain track pitch is performed.
[0028]
The wavelength of the laser 14 used for exposure is not particularly limited as long as it is 450 nm or less, and an argon ion laser of 413 nm and 361 nm and a krypton ion laser of 351 nm can be suitably used. The beam diameter enlarged by the beam expander 17 and the performance of the objective lens 18 are important factors that determine the size of the focal point.
[0029]
After this recording step, the exposed portions are removed by a developing solution mainly composed of an alkaline aqueous solution, and a pit pattern 20 based on the formatter signal appears on the glass plate 11 as shown in FIG. As the developer at this time, an inorganic developer containing sodium or potassium, an organic developer typified by an aqueous solution of tetramethylammonium hydroxide, or the like is used.
[0030]
Next, as shown in FIG. 2C, a Ni thin film 22 is formed on the surface of the pit pattern 20 by a sputtering method. Next, as shown in FIG. The nickel plate 23 is formed by plating and making the electrode thicker. After that, the nickel plate 23 is peeled off from the glass plate 11, and the back surface is polished and the inner and outer diameters are processed, so that the stamper 21 is manufactured. The pit 1 of the stamper 21 is a projection, although it is contrary to the literal meaning.
[0031]
Next, as shown in FIG. 2E, a stamper 21 made of Ni is set on metal frames 24a and 24b of an injection molding machine to form a mold, and a polycarbonate resin 26 is injected into a cavity of the mold. By pressing and cooling the optical disk 25, the optical disk 25 on which the shape of the pit 1 of the stamper 21 is transferred is formed.
[0032]
The shape of the pits 1 of the stamper 21 mainly depends on the type and thickness of the resist for coating and forming the resist layer 12, the beam diameter introduced into the objective lens 18 in the LBR 13, the performance of the objective lens 18, and the laser output from the laser 14. It is controlled by the wavelength of light, development conditions in the development process, and the like.
[0033]
In particular, as a method of controlling the inclination angle of the side surface of the important pit 1, it is effective to use a resist having a low γ value. That is, the inclination angle is reduced by using a beam having a low γ value in combination with the wavelength of the exposure beam to be used. Also, by lowering the magnification of the beam expander 17 provided in the LBR 13 to be used, the inclination angle of the side surface of the pit 1 when forming the same pit width can be reduced. When the exposure power is reduced and the development time is increased, the residual film ratio of the unexposed resist in the development step is reduced, the contrast is reduced, and the inclination angle of the side surface of the pit 1 is reduced.
[0034]
In the present embodiment, by optimally combining these conditions, the following pit shapes are created, whereby the transferability and releasability during molding are good, and the signal characteristics on the disc are good, The stamper 21 which satisfies both of the above characteristics is created.
[0035]
That is, in FIG. 1, among the pits 1 on the surface of the stamper 21 made of Ni as a base, the width of each pit 1 is set to W _3T , W _L , and the height of the pit 1 for 3T pits and long pits of 8T or more. the _H 3T, _{H L,} the inclination angle _AR 3T radial pit sidewalls, AR _L, in the tangential direction of the pit sidewall inclination angle _aT 3T, as aT _L, are those having the following shape. Here, the width of the pit 1 is a width at half the pit height (FWHM: Full Width At Half Maximum).
[0036]
For the 3T pit, 200 nm ≦ W _3T ≦ 270 nm
120 nm ≦ H _3T ≦ 160 nm
40 degrees ≦ AR _3T ≦ 55 degrees 30 degrees ≦ AT _3T ≦ 50 degrees For long pits, 200 nm ≦ W _L ≦ 280 nm
120 nm ≦ _HL ≦ 160 nm
40 ° ≦ A _L ≦ 55 ° 30 ° ≦ AT _L ≦ 55 ° and | W _L −W _3T | ≦ 30 nm
The pit shape satisfies the following conditions.
[0037]
3T pit width _{W 3T} exceeds the 270 nm, tilt angle _AR 3T in the radial direction or pit sidewall long pit width _{W L} exceeds 280 nm, the AR _L exceeds 55 degrees, reduces the releasability of the molding process In this case, a whitish area commonly called a cloud is easily generated on the surface of the DVD disk. This is determined to be NG in the defect inspection of the disk, and is the main cause of a decrease in yield. Further, a pit width _W 3T, _{W L} can not be obtained having good electric signal characteristic at an inclination angle _AR 3T in the radial direction of 200nm or less than the pit sidewalls, AR _L is less than 40 degrees. Preferably, the long pit width _{W L} is 230nm or 260nm or less, and the inclination angle _AR 3T in the radial direction of the pit sidewalls, AR _L is less than 53 degrees 40 degrees. Tilt angle AT 3T in the tangential _direction, as the AT _L, less than 50 degrees in the 3T pit to ensure the releasability, it is necessary in the long pit is less than 55 degrees, preferably not more than 45 degrees 30 degrees It is. If the angle is less than 30 degrees, of the signal characteristics of the disk, the jitter is large and the characteristics are degraded, and a good signal characteristic cannot be obtained.
[0038]
Next, specific examples and comparative examples will be described.
[0039]
(Example)
A positive resist was applied by spin coating to a φ200 glass plate that had been precisely polished and cleaned. After coating, baking was performed on a hot plate at 80 ° C. for 10 minutes to remove the solvent component in the resist layer. At this time, the layer thickness was measured by an ellipsometer and was 148 nm. The glass plate was exposed by LBR. For exposure at this time, a 351 nm krypton laser manufactured by Coherent was used, the formatter signal was modulated by AOM, and the beam was expanded by a beam expander and introduced into the objective lens. This glass plate was developed using an organic developer (NMDW) manufactured by Tokyo Ohka Chemical Co., Ltd., with an objective lens having a NA of 0.9, and a pit pattern was developed by removing the resist in the exposed area. Thereafter, a Ni thin film is formed on the surface of the pit pattern by a sputtering method, and furthermore, the thin film layer is electroded and plated in a plating step, the nickel film is formed into a thicker film, and peeled from the glass plate. Back stamping and inner and outer diameter processing were performed to obtain a stamper.
[0040]
The pit shape at this time was measured by AFM. After confirming that there was no change in the pit shape on the inner and outer circumferences of the stamper, the measurement was performed on the middle circumference, and 10 samples of 3T pits and 8T or more long pits were measured. Was made the pit shape of this stamper. As a result, the 3T pits and 8T or more long pit width _W 3T of each pit, _{W L,} the height _H 3T pit, _{H L,} the inclination angle _AR 3T radial pit sidewalls, AR _L , the inclination angle of the tangential direction of the pit sidewalls _aT 3T, as aT _L, were as follows.
[0041]
Regarding the 3T pit, W _3T : 255 nm
H _3T: 145nm
AR _3T: 48 degrees _AT 3T: 38 degrees for long _pit, W L: 265nm
_HL : 145 nm
AR _L: 52 degrees _AT L: 42 degrees a and | _W L _-W 3T |: 10nm
Injection molding of a DVD optical disk with polycarbonate resin using this stamper revealed no defects due to mold release failure and good transfer. Also, the signal characteristics of the optical disc were very good, with the jitter being 6.8% against the standard 8%.
[0042]
(Comparative example)
A positive resist for I-ray (ultraviolet light) was applied to a glass plate having a diameter of 200 by a spin coating method in the same manner as in the above-described example, baked under the same conditions as in the example, and measured with an ellipsometer. The layer thickness was 140 nm. This glass plate was exposed with the same LBR as in the example. Further, development was performed under the same developing conditions as in the example, and a stamper was formed using the same process. The pit shape at this time was measured by AFM using the same method as in the example, and the following results were obtained.
[0043]
Regarding the 3T pit, W _3T : 290 nm
_H3T : 135 nm
AR _3T: 58 degrees _AT 3T: about 58 degrees long _pit, W L: 335nm
_HL : 135 nm
AR _L: 61 degrees _AT L: 58 degrees a and | _W L _-W 3T |: 45nm
Molding was performed using this stamper. The disc had good signal characteristics with a jitter of 7.2% compared to the standard of 8%, but a defect called a cloud due to poor mold release occurred frequently. Further, although the defects were reduced by changing the molding conditions, the production was extremely low in yield.
[0044]
【The invention's effect】
According to the present invention, by optimizing the pit shape of the stamper as described above, it is possible to greatly reduce the occurrence of defects due to poor mold release in the molding process, and to obtain good optical disk signal characteristics. Can be obtained. As a result, the yield in the manufacturing process can be greatly improved, and the excellent characteristics of DVD, which is capable of mass production at low cost, can be maximized. Demonstrate useful effects.
[Brief description of the drawings]
1A and 1B show a pit shape in one embodiment of a stamper of the present invention, wherein FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along the line AA of FIG. 1A, and FIG. FIG.
FIG. 2 is an explanatory diagram of a stamper of the embodiment and a process of manufacturing an optical disc using the stamper.
FIG. 3 is an explanatory diagram of an exposure process by the laser beam recording device in the embodiment.
FIG. 4 is an explanatory diagram of a γ value of a resist.
[Explanation of symbols]
Reference Signs List 1 pit 11 glass plate 12 resist layer 20 pit pattern 21 stamper 22 nickel thin film 23 nickel plate 25 optical disk W pit width H pit height AR inclination angle of pit sidewall in radial direction AT inclination angle of pit sidewall in tangential direction

Claims (4)

About 3T pits and 8T or more long pit, the respective widths _W 3T, _{W L,} the height _H 3T pit, _{H L, AR} 3T an inclination angle in the radial direction of the pit sidewalls, AR _L, Tangier pit sidewalls The inclination angles in the tangential direction are AT _3T and AT _L ,
For the 3T pit, 200 nm ≦ W _3T ≦ 270 nm
120 nm ≦ H _3T ≦ 160 nm
40 degrees ≦ AR _3T ≦ 55 degrees 30 degrees ≦ AT _3T ≦ 50 degrees For long pits, 200 nm ≦ W _L ≦ 280 nm
120 nm ≦ _HL ≦ 160 nm
40 ° ≦ A _L ≦ 55 ° 30 ° ≦ AT _L ≦ 55 ° and | W _L −W _3T | ≦ 30 nm
A stamper characterized by a pit shape that satisfies the requirements. The stamper according to claim 1, wherein nickel is used as a base material. A pit pattern having a pit shape according to claim 1 is formed on a resist layer formed on a surface of a glass plate, a metal thin film is applied to the surface, the surface is subjected to a conductive treatment, and then a nickel plate is formed by nickel plating. A method for manufacturing a stamper, comprising: removing a substrate from a glass plate and washing the stamper. An optical disk manufactured by injection molding using the stamper according to claim 1 or 2 as a mold.

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