JP2005228387A - Method for manufacturing master optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a master optical disk having a steep side wall and a pattern high in rectangularity. <P>SOLUTION: In the master optical disk using RIE (reactive ion etching), a resist stored in air at a room temperature is subjected to exposure and development for 200 to 400 hours, preferably 350 hours to make a pattern in which the end of a land projects, and the RIE is carried out by using the resist pattern as a mask. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing an optical disc master used for producing a substrate of an optical information recording medium, and particularly, when a substrate such as a digital audio disc, a write-once disc, a rewritable disc is manufactured by injection molding. The present invention relates to a manufacturing method for producing a stamper to be used.

  Various attempts have been made to improve the recording density of optical discs. For example, Japanese Patent Laid-Open No. 6-290496 proposes an increase in the density of magneto-optical recording by a domain wall displacement detection (hereinafter referred to as DWDD) method. In the DWDD system, it is possible to obtain a reproduction resolution exceeding the limit restricted by the light spot diameter in the line (track) direction by utilizing the phenomenon of domain wall movement due to the temperature gradient generated by the readout light spot. By combining this with land groove recording, the surface recording density can be dramatically improved as compared with conventional magneto-optical recording.

  Further, in the land / groove recording, as a device for facilitating the domain wall movement, it is effective to use a substrate having a steep side wall (taper between the land and the groove). If a magnetic film is formed on the substrate by a highly directional film forming method, the magnetic film can be substantially prevented from being deposited on the side wall. As a result, it is possible to form a magnetic domain having substantially no domain wall on the side wall portion with respect to each of the land portion and the groove portion, and the track is magnetically divided and the domain wall movement is likely to occur.

  In addition, preventing the magnetic film from being deposited on the side wall portion is also effective in suppressing thermal interference with adjacent tracks and improving cross erase resistance. At the same time, the DWDD system can be expected to suppress crosstalk from adjacent tracks during reproduction. This is because it is possible to prevent the adjacent tracks from being heated above the domain wall motion start temperature Ts during reproduction. For this reason, in the magnetic domain recorded in the adjacent track, the domain wall motion does not occur and normal magneto-optical reproduction is performed. However, if the recording mark is set to a size smaller than the resolution of the light spot, a large crosstalk is caused. Will not occur.

  The combination of the deep groove substrate and the DWDD method can drastically improve the surface recording density due to the synergistic effect of the magnetic track segmentation effect, the cross erase resistance improvement, and the crosstalk suppression effect described above ( For detailed explanation, refer to Journal of Applied Magnetics Society of Japan, Vol.23, No.2, 1999, p764-769, Shiratori “High Density of Magneto-Optical Disk by Domain Wall Movement Detection Method”.

As described above, a method using reactive ion etching (hereinafter referred to as RIE) is described in Japanese Patent Application Laid-Open No. 7-161080 as a method for manufacturing a substrate having a steep taper portion having good characteristics with respect to domain wall motion. At present, this method is a common method for manufacturing an optical disc master.
Japanese Patent Laid-Open No. 7-161080

  However, when RIE is performed on quartz using a photoresist as a mask, it is generally difficult to obtain a good selection ratio. In JP-A-7-161080, in order to solve the problem that the side wall roughness between the land and the groove deteriorates the releasability at the time of 2P molding or injection molding, RIE with a high selection ratio is used. Side wall roughness is suppressed. In order to improve the selection ratio, an etching gas is appropriately selected, and RIE is performed at a low gas pressure and a low RF power. Even if such improvement measures are taken, the selectivity ratio between resist and quartz is several to one. It was only improved to a certain extent. Therefore, it is inevitable that the resist mask itself is etched during the etching and the mask is retracted.

  From the aspect of resolution, a positive type photoresist is generally used in photolithography. However, due to the characteristics of the positive type resist, the side wall angle of the mask pattern becomes gentle during normal exposure.

  As a result, it is difficult to produce a resist mask having a steep side wall and good rectangularity as a normal resist mask, and also in RIE in which the shape of the resist mask is reflected in the shape after etching, It is difficult to produce a master with good rectangularity. This not only prevents obtaining good characteristics in the domain wall motion detection type optical disk studied by the present inventor, but also reduces the effective width of the land portion, thereby recording in land groove recording. It also hinders the improvement of density.

  Further, in Japanese Patent Laid-Open No. 7-161080, a resist film having a thickness of 200 nm or more is used to make the side wall of the resist mask pattern steep, and the side wall of the glass master after RIE is made steep. However, uneven exposure occurs due to the thick resist, and the land groove duty ratio tends to vary. Due to the variation in duty ratio, the amount of reflected light changes between the land and the groove, and as a result, noise is generated in the reproduction signal of the manufactured optical disk.

  As a method of improving the rectangularity of the pattern after RIE, a method of performing RIE after projecting the end of the land from a normal mask shape is considered. No. 348387 describes a method of exposing the central portion of the portion corresponding to the land of the previous pattern after exposure of the guide groove with lower power than the previous pattern. However, this method is also technically difficult in terms of exposure variations due to the thick resist and alignment of double exposure.

  The present invention has been made in view of the above problems, and in a method of manufacturing an optical disc master, a positive photoresist is applied on a quartz substrate, and a guide groove pattern is exposed using a laser beam. The laser beam is a guide. By scanning and exposing only the groove portion and not exposing between the guide grooves, the end portion of the resist remaining after development is protruded from the central portion, and then reactive ion etching is performed using the resist pattern as a mask. Etching is performed on the quartz substrate in the portion where the metal is removed to form a guide groove, and the resist remaining after the reactive ion etching is removed.

  As described above, according to the present invention, in manufacturing an optical disc master using RIE, exposure and development are performed on a resist stored in air at 200 to 400 hours, preferably 350 hours or more, at room temperature. A pattern with protruding end portions is prepared, and RIE is performed using the resist pattern as a mask, thereby making it possible to manufacture an optical disc master having a steep sidewall and a rectangular pattern. Compared to a normal resist mask that does not protrude the end, the same steep sidewall can be produced with a thin resist film thickness, so that it is less susceptible to exposure variations, and as a result, an optical disc with a low noise level can be produced. It is.

  When the DWDD magneto-optical medium and the substrate manufactured according to the present invention are combined, the side walls become steep so that good track separation is achieved, and the domain wall can be smoothly moved in the land portion and the groove portion. Crosstalk and cross erase can be suppressed, and signal jitter during signal reproduction can be greatly improved.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 is a process diagram showing a method of manufacturing an optical disc master according to the present invention. In the method of manufacturing an optical disc master according to the present invention, the following steps are performed:
A step (1) of applying a positive photoresist on a quartz substrate.
● A step (2) of storing a resist-coated quartz substrate in room temperature and air.
A step (3) of exposing a guide groove pattern by irradiating a light-coated light onto a resist-coated quartz substrate stored for a certain period
A step (4) of developing the exposed guide groove pattern.
A step (5) of forming a guide groove pattern on a quartz substrate by performing reactive ion etching using the developed resist as a mask.
A step (6) of removing the residual resist mask by oxygen ashing or the like. The optical disc master is completed.

  FIG. 1 shows a manufacturing process of an optical disc master.

  First, a glass plate 1 (manufactured by Asahi Glass Co., Ltd.) serving as an optical disc master was washed. The contents of the cleaning step were spin cleaning using acetone and pure water, and oxygen ashing was performed using an ashing device (RH-20 manufactured by ULVAC). The ashing conditions at this time are RF power of 150 W, gas flow rate of 80 sccm, pressure of 8.0 Pa, and time of 30 seconds. Thereafter, it was washed again using acetone and pure water under the same conditions as before ashing, and baked in a clean oven. The baking conditions are a temperature of 50 ° C. and a time of 1 hour. Finally, it was left to cool at room temperature for 1 hour.

  Subsequently, a coupling agent (HMDS) was applied to increase the adhesion between the glass plate and the resist. Thereafter, baking was performed at a temperature of 50 ° C. for a time of 1 hour and left to cool at room temperature for 1 hour.

  Subsequently, resist 2 was applied by a spinner. The thickness of the applied resist is about 40 nm. Then, after baking at a temperature of 90 ° C. and a time of 30 minutes, those were allowed to stand in air at room temperature for 24 hours, 100 hours, 200 hours, and 350 hours.

  After that, using a cutting machine (manufactured by Yoshikawa Seimitsu Engineering Co., Ltd.) using an Ar ion laser (manufactured by Nippon Laser Co., Ltd., wavelength 351 nm) as an exposure beam 3, a track pitch of 0.72 μm in a range 7 from a radial position of 16 mm to 21.9 mm A guide groove having a track pitch of 0.64 μm was exposed in a range 8 from a radial position of 23 mm to 28.9 mm. The exposure conditions at this time were such that the rotation speed was constant at 600 rpm and the exposure power was such a power that a desired duty ratio was obtained. Patterns having different duty ratios were exposed for 6 zones in each zone within each range. FIG. 2 shows an exposure pattern formed on a resist-coated substrate.

Thereafter, 2.38% NMD-3 (Tokyo Ohka's resist developer) and ultrapure water were mixed at a volume ratio of 11: 8 and diluted with a spinner (Nihon Laser Co., Ltd.). Thus, the resist 4 in the exposed portion was removed and the end portion of the resist 5 in the unexposed portion was protruded. The development conditions at this time are pre-pure water application at 100 rpm for 300 seconds, developer solution application at 100 rpm for 30 seconds, post-pure water rinse at 150 rpm for 300 seconds, and N ₂ blow at 900 rpm for 60 seconds. 3 to 6 are AFM images of resist masters in which the pattern was exposed and developed after storage for 24 hours, 100 hours, 200 hours, and 350 hours, respectively.

  Thereafter, the resist residue on the groove surface was removed by oxygen ashing using an ashing device (RH-20 manufactured by ULVAC). The ashing conditions at this time are RF power of 30 W, gas flow rate of 20 sccm, pressure of 3.0 Pa, and time of 20 seconds.

Next, reactive ion etching was performed using a reactive ion etching apparatus (DEA-506 manufactured by Anelva). A quartz block was placed in the vacuum chamber, a polycarbonate plate coated with resist was laid under the sample, and CHF ₃ gas was used. Etching conditions at this time are RF power of 200 W, gas flow rate of 30 sccm, pressure of 3.0 Pa, and time of 7.5 minutes.

  Thereafter, the remaining resist was removed by oxygen ashing using an ashing device (RH-20 manufactured by ULVAC). The ashing conditions at this time are RF power of 150 W, gas flow rate of 80 sccm, pressure of 8.0 Pa, and time of 90 seconds.

  The optical disc master 6 was produced by the above process. Table 1 shows the result of measuring the side wall angle of the shape using AFM (Nanoscope-III manufactured by Digital Instruments). The side wall angle at this time is an angle based on the bottom of the groove, and in the case of a complete rectangle, the side wall angle is 90 °.

  As shown in Table 1, a steep side wall can be produced when the resist storage time exceeds 200 hours, and a steep side wall can be produced when the resist storage time exceeds 350 hours. On the other hand, when the resist storage period exceeded 400 hours, the protrusion at the end of the groove was reduced, and the side wall angle was the same as that for storage for 200 hours. In addition to the measurement results shown in FIGS. 3 to 6, in order to create a guide groove having good rectangularity, the protrusion at the end of the resist should be 1/2 or more of the resist thickness at the center of the land. Obtained the desired result.

  Further, as a result of combining the DWDD type magneto-optical medium and the substrate manufactured by this example, crosstalk and cross erase can be suppressed, and signal jitter during signal reproduction can be greatly improved.

<Comparative example>
For comparison, an optical disc master 6 was produced by the same method as in the example. However, the resist-coated substrate was exposed immediately after resist coating, baking, and cooling without being stored in air at room temperature. As a result of measuring the shape using AFM (Nanoscope-III manufactured by Digital Instruments), the side wall angle of the pattern was 45 ° to 50 °. In addition, as a result of combining the DWDD type magneto-optical medium and the substrate manufactured by this comparative example, suppression of crosstalk and cross erase and improvement of signal jitter during signal reproduction were not achieved.

Optical disc master production process Exposure pattern Resist master AFM image exposed after 24 hours storage Resist master AFM image exposed after storage for 100 hours Resist master AFM image exposed after 200 hours storage Resist master AFM image exposed after storage for 350 hours

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Positive type photoresist 3 Exposure beam 4 Exposed part photoresist 5 Unexposed part resist 6 Optical disk original disc 7 Track pitch 0.72 micrometer pattern 8 Track pitch 0.64 micrometer pattern

Claims (5)

  In a method of manufacturing an optical disc master, a positive photoresist is coated on a quartz substrate, and a guide groove pattern is exposed using a laser beam. The laser beam scans and exposes only the guide groove portion, and scanning exposure is performed between the guide grooves. By performing the reactive ion etching using the resist pattern as a mask, the quartz substrate in the portion where the resist is removed is etched. A method for manufacturing an optical disc master, characterized in that a guide groove is formed by the above-described method and a resist remaining after reactive ion etching is removed.   2. The method of manufacturing an optical disc master according to claim 1, wherein a photoresist stored in the photoresist for a certain period is used.   3. The method of manufacturing an optical disc master according to claim 2, wherein a photoresist stored at room temperature in air for 200 hours to 400 hours is used as the photoresist.   2. The method of manufacturing an optical disk master according to claim 1, wherein after the photoresist is applied, the optical disk master is stored in air at room temperature for 200 hours to 400 hours.   2. The method of manufacturing an optical disc master according to claim 1, wherein the development is spin development.

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