Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2002-05-17
2004-10-12
Lorengo, Jerry A (Department: 1734)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S002000, C134S004000, C156S094000, C156S247000, C156S272200, C156S345420
Reexamination Certificate
active
06802321
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates in general to a master medium cleaning method, and in particular to a method of cleaning magnetic transfer master mediums, which are used to perform magnetic transfers, or optical disk master mediums, which are used in manufacturing optical disks.
2 Description of the Related Art
A magnetic transfer method is a method comprising the steps of: bringing a master medium, on which a transfer pattern has been formed, into close contact with a slave medium, which has been provided with a magnetic recording portion for receiving the transfer, to form a conjoined body; and applying a transfer magnetic field to the conjoined body so as to transfer and record the magnetic pattern corresponding to the transfer data (such as servo signals) onto the slave medium. This magnetic transfer method has been described in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566, for example.
The master medium employed in the magnetic transferred is formed of a silicon substrate or a glass substrate, for example, on the surface of which an uneven pattern composed of a magnetic body is formed by use of a photo lithography process, a sputtering process, an etching process, or the like. Further, magnetic transfer master mediums can also be manufactured by use of a lithography technology such as that used in the manufacture of semiconductors, or a stamping technology such as that used in the manufacture of optical disks.
In order to improve the quality of the magnetic transfer described above, it is necessary that the slave medium and the master medium be conjoin so that no gap whatsoever exists therebetween. That is to say, if there are contact deficiencies therebetween, regions on which a magnetic transfer can not be performed occur; if a magnetic transfer can not be performed, signal omissions occur in the magnetic data transferred to the slave medium and the signal quality thereof is reduced, and for cases in which the transferred data are servo signals, an adequate tracking function can not be obtained, whereby a problem arises in that the reliability is reduced.
However, when performing magnetic transfers according to the magnetic transfer method described above, the surface of the master medium becomes littered with foreign matter that becomes attached thereto through the repeated usage thereof. This foreign matter can consist of dust, fiber strands and other debris originating in the surrounding environment.
If a magnetic transfer is performed when there is dust or other debris attached to the surface of the master medium, adequate contact between the area of the surface of the master medium centering on the dust or debris attached thereto and the surrounding vicinity thereof and the corresponding area of the slave medium cannot be ensured; whereby a pattern of a predetermined signal level cannot be transferred, and the transfer quality becomes deteriorated thereby. By repeatedly bringing a master medium, onto the surface of which foreign matter has become attached, into close contact with slave mediums, the attachment strength of the foreign matter to the surface of the master medium is heightened; whereby deficiencies in pattern transfer of the same or greater magnitude are repeated during the performance of magnetic transferences to slave mediums subsequently brought into close contact with said master medium, and said foreign matter becomes the cause of multiple faulty products. Further, the surface of the master medium becomes deformed by this attached debris, and a problem arises in that the proper functionality thereof is lost.
In this regard, cleaning technology, wherein a cleaning disk to which a cleaning pad has been attached is rotated while in contact with the surface of the master medium to remove dust and debris that have become attached thereto has been proposed as described in Japanese Unexamined Patent Publication No. 2000-285637, for example.
However, in performing cleaning using cleaning technology such as that described above, for cases in which the transfer pattern formed on the data bearing surface of the master medium is provided as an uneven form, foreign matter becoming lodged in the depression portions thereof is difficult to remove. Further, there are cases such as those in which foreign matter originating in the surrounding environment becomes embedded in the depression portions, cases in which the surface of the master medium becomes marred or scratched due to foreign matter, and cases in which it is not possible to remove minute particulate foreign matter that has become adhered to the surface of the medium, giving rise to a fear that transfer deficiencies caused thereby will not be corrected due to the inadequacy of the cleaning process. In particular, because master mediums are expensive, from the standpoint of cost, it is advantageous that the master mediums be reusable and have a long life span.
Further, cleaning methods performed before the magnetic transfer process in order to remove foreign matter that has become adhered to the surface of the master medium, such as an ultrasound cleaning using a cleansing liquid, a wiping cleaning, or the like can also be considered. However, it is possible that the foreign matter removed thereby becomes re-adhered after performing a cleansing by one of these methods, that the removal of the foreign matter is insufficient, that a watermark occurs on the surface of the master medium when the cleansing liquid has dried, or that the surface of the master medium becomes marred or scratched due to abrasion by the wiping material, giving rise to a fear that these become the origin of damage to the master medium, and that transmission deficiencies occur in the transferred signal. That is to say, even if foreign matter adhered to the surface of the master medium is temporarily removed by use of a cleansing liquid, a wiping material or the like, there are cases in which foreign matter in the form of washing liquid remaining on the surface of the master medium, or foreign matter from the wiping material becomes attached to the surface of the master medium; in particular, it is not possible to remove some of the minute particulate foreign matter that has become adhered to the surface of the medium.
When performing a magnetic transfer, the master medium and the slave medium are put into close contact with each other and a magnetic field is applied to the mediums to magnetically transfer the shape of the pattern of the master medium onto the slave medium. If something remains between the master medium and the slave medium in this process, an air gap is formed between the mediums and transmission deficiencies occur. This was discovered by inspecting the master medium that was reused after washing by the above-mentioned cleaning method. That is, it was discovered that the number of surface defects was increased by the cleaning method. There are cases in which the signal omissions occurring due to foreign matter having become adhered to the surface of the master medium in the course of the above-described magnetic transfer are present from the initial stages thereof when slave mediums are exchanged one after the other and the magnetic transfer is performed a plurality of times in succession. It has been determined that this is due to foreign matter that has become adhered to the surface of the master medium during the manufacture thereof. Further, analysis of the attached foreign matter has shown that the foreign matter is composed of organic matter; the foreign matter has been determined to be formed of the same source material as the coating material used to form the protective layer provided over the pattern of the substrate of the master medium.
More specifically, as described above, a pattern corresponding to the transfer signal is formed on the surface of the master medium, and a magnetic layer is formed over said pattern; because the pattern forming process and the magnetic layer forming process are performed se
Kamatani Akito
Nishikawa Masakazu
Fuji Photo Film Co. , Ltd.
Lorengo Jerry A
Sughrue & Mion, PLLC
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