Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article
Reexamination Certificate
2000-12-05
2004-11-09
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Light polarizing article or holographic article
C264S001370, C264S002500, C425S810000
Reexamination Certificate
active
06814897
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods for making molding tools. More particularly, the molding tools are used for molding a resin substrate which has fine pits, i.e., concavities and protuberances and to a method for manufacturing a resin substrate. Such resin substrates may be used as an optical disk, a magnetic disk, a hard disk, etc., for recording data.
It is an object of this invention to identify a son stamper and an optical disk that have been manufactured using that son stamper and a particular master substrate.
BACKGROUND OF THE INVENTION
Data recording media such as optical disks, hard disks, etc., are capable of recording large quantities of information. Such data recording media are commonly referred to as CD's (compact disks), LD's (laser disks), DVD's (digital video disks, digital versatile disks), etc. These data recording media may contain music, movies, software, etc. Such media are also used as storage devices in computers. Demand for such recording media is expanding greatly. Indeed, it is anticipated that optical disk and hard disk usage will continue to expand since these are the major recording media of the multimedia age.
Optical disks are classified according to the existence or absence of a recording layer and further classified according to the type of recording layer. Optical disk types include: (1) the read-only type (CD, LD, CD-ROM, photo-CD, DVD-ROM, read-only type MD, etc.); (2) the write-once type (CD-R, DVD-R, DVD-WO, etc.); and (3) the rewriteable type capable of erasure followed by writing any number of times (magneto-optical disk, phase-change type disk, MD, CD-E, DVD-RAM, DVD-RW, etc.). Moreover, the high density HD-DVD has also been proposed as a medium of the future.
The process for manufacturing these optical disks begins with the molding of raw material resin into a resin substrate. Raw material resin, for example, polycarbonate, acrylate resin, polystyrene, etc., is heated, melted or partially melted, and then pressed using a stamper, thereby molding (manufacturing) a resin substrate. Typically, the molding method used is a pressure molding or injection molding method. The stamper forms fine concavities and protuberances which represent the information to be copied upon the substrate surface. Other than resin molding, there is no such method for manufacturing large quantities of substrates that have minute concavities and protuberances in a short time period.
Types of pits and protuberances include pits that indicate a unit of information and guide grooves that are provided for tracking by the pickup head. Generally, the manufacture of data recording media involves circular substrates provided with pits and grooves on the substrate surface in a pattern of concentric circular rings or as a spiral pattern. The region between grooves along the radial direction is called a “land.” Recording upon the lands occurs during the land recording method, or alternatively, recording occurs within the groove per the groove recording method.
In order to improve the recording density, the land/groove recording method was developed to record upon both the grooves and lands. In this case, both grooves and lands are tracks, and the width of both grooves and lands are nearly equal. However, there are reasons for sometimes deliberately widening one or the other. For example, when incident light enters the backside surface (flat smooth surface) of the substrate, what appears as a land from the substrate interior side becomes a groove as seen from the substrate front.
As the recording density has increased, to meet the increased need for storage capacity, the width of grooves, lands, and pits has decreased and their depth has increased. For example, the width has decreased from <1 &mgr;m to <0.3 &mgr;m and the depth has increased from >40 nm to >250 nm. As the width decreases and the depth increases (i.e., as density become higher), molding of the resin substrate becomes increasingly difficult, and the yield of good product declines.
When manufacturing a hard disk, a magnetic recording layer is typically formed or deposited on an aluminum or glass substrate with recording carried out by a magnetic head. A reflection layer, a recording layer and a protection layer may then be formed on the resin substrate to produce the desired final product.
As recording density increases, the recording layer becomes extremely flat and smooth. When the magnetic head becomes relatively still, the recording head and the recording layer adhere to one other and then fail to separate. In order to avoid this phenomenon, a garage region (CSS region=contact stop and start) is provided. The surface of this garage region is deliberately finished with a rough texture using a laser such that surface adherence is prevented. Head tracking also becomes difficult as recording density increases. Therefore it is proposed that a magnetic hard disk, like an optical disk, should be provided with grooves. Due to the demand for such roughness and grooves, resin substrates are proposed as a means to increase manufacturing productivity. Increased productivity results due to the formation of roughness and grooves during the substrate molding. Resin substrates are also said to be advantageous due to their light weight.
Previously, molding tools were manufactured by the process described in Hunyar, U.S. Pat. No. 4,211,617, which corresponds to Japanese Publication Koukoku Sho 59-16332, the disclosures of which are incorporated by reference herein in their entirety. A comparison of the method of forming the molding tool as disclosed in Hunyar and that of the present invention is provided in
FIGS. 3A
(present invention) and
3
B (Hunyar).
Generally, molding tools are manufactured using a glass substrate that is polished with the precision of an optical surface. After the substrate
1
is cleaned it is coated with a primer, for example, a silane coupling agent. A photoresist is then applied by spin coating and subjected to a pre-bake process. Positive-type, i.e., wherein the region exposed to light is removed during development, photoresist
2
is often used (see item (B
1
) in FIG.
3
). Next, a laser beam recorder or a laser cutting machine is used to expose the photoresist
2
with a pattern of pits and/or grooves where the width of pits and grooves is generally determined by the laser beam diameter and the depth of the pits and grooves is generally determined by the photoresist thickness. When the exposed photoresist is developed, a resist pattern of pits and/or grooves is obtained upon the substrate surface. Following development, the resist pattern may optionally undergo a 20-60 minute post-bake at 80-120° C. When such a post-bake is used, the resist pattern is then cooled down to room temperature. Roughly 10 hours are required to cool the resist pattern. The resist pattern formed in this manner is referred to as a “master substrate” or a “master” and is indicated by item (B
2
) in
FIG. 3
of the present application. It is also shown in
FIG. 4
, reference number
46
, of Hunyar U.S. Pat. No. 4,211,617. In addition to the fact that these master substrates require long production times, the laser beam recorder or a laser cutting machine used to expose the photoresist is very expensive. As a result, master substrates are expensive and time-consuming to produce.
The master substrate then undergoes metallization treatment to form a conductive layer on the surface. Generally such treatment is carried out by sputtering (dry-type method), or by non-electrolytic plating (wet-type method). Following metallization, a thick plating layer, such as nickel (Ni), is formed upon the master substrate. The result is a first metallic molding tool that has a double layer structure that consists of a conductive layer and the Ni plating layer. This is shown by item (B
3
) of
FIG. 3
of the present application. This first metallic molding tool is referred to herein as the “father,”
3
. A free father is obtained when the father
3
is peeled from the master substrate
Discovision Associates
Do Caroline
Masaki Keiji
Vargot Mathieu D.
Wong Steve
LandOfFree
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