Coating apparatus – Gas or vapor deposition
Reexamination Certificate
2000-03-16
2004-05-11
Alejandro-Mulero, Luz (Department: 1763)
Coating apparatus
Gas or vapor deposition
C118S7230FI, C156S345290, C156S345330
Reexamination Certificate
active
06733590
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for multilayer ion beam deposition (IBD) utilizing a common ion beam source for depositing each constituent layer of the multilayer. The inventive method and apparatus enjoy particular utility in the manufacture of magnetic and/or magneto-optical (MO) data recording/information storage and retrieval media, e.g., hard disks, wherein, as part of the manufacturing methodology, multilayer protective overcoats are deposited over the recording media layer(s) for providing abrasion resistance and protection from environmentally-induced degradation, e.g., corrosion.
BACKGROUND OF THE INVENTION
A magnetic recording medium, e.g., a hard disk, typically comprises a laminate of several layers, including a non-magnetic substrate, such as of aluminum-magnesium (Al-Mg) alloy or a glass, ceramic, or glass-ceramic composite material and formed sequentially on each side thereof: a polycrystalline underlayer, typically of chromium (Cr) or, Cr-based alloy, a polycrystalline magnetic recording medium layer, e.g., of a cobalt (Co)-based alloy, a hard abrasion-resistant, protective overcoat layer, typically carbon (C)-based, and a lubricant topcoat layer. Magneto-optical (MO) media, e.g., in disk form, similarly comprise a laminate of several layers, including reflective, dielectric, thermo-magnetic, protective overcoat, and lubricant topcoat layers.
In operation of e.g., the magnetic recording medium, the polycrystalline magnetic recording medium layer is locally magnetized by a write transducer, or write head, to record and store information. The write transducer creates a highly concentrated magnetic field which alternates direction based upon the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium, then the grains of the polycrystalline recording medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of magnetization matches the direction of the applied magnetic field. The magnetization of the polycrystalline recording medium can subsequently produce an electrical response in a read transducer, allowing the stored information to be read.
Thin film magnetic and MO recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (CSS) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance above the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, thereby allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
As a consequence of the above-described cyclic CSS-type operation, the surface of the disk or medium surface wears off due to the sliding contact if it has insufficient abrasion resistance or lubrication quality, resulting in breakage or damage if the medium wears off to a great extent, whereby operation of the disk drive for performing reading and reproducing operations becomes impossible. The protective overcoat layer is formed on the surface of the polycrystalline magnetic recording medium layer so as to protect the latter from friction and like effects due to the above-described sliding action of the magnetic head. Abrasion-resistant, carbon (C)-containing protective coatings have been utilized for this purpose, and are typically formed by sputtering of a carbon target in an argon (Ar) atmosphere. Such amorphous carbon (a-C)-containing protective overcoat layers formed by sputtering have relatively strong graphite-type bonding, and therefore exhibit a low coefficient of friction in atmospheres containing water (H
2
O) vapor, which characteristic is peculiar to graphite. However, the a-C layers produced in such manner have very low hardness as compared with many ceramic materials such as are employed as slider materials of thin film heads, and thus are likely to suffer from wear due to contact therewith.
In recent years, therefore, carbon-based protective overcoat layers having diamond-like hardness properties (i.e., HV of about 1,000-5,000 g/mm
2
) have been developed, and films of diamond-like carbon (DLC) having a high percentage of diamond-type C—C bonding have been utilized. Such DLC films exhibit a high degree of hardness due to their diamond-like sp
3
bonding structure, and in addition, exhibit the excellent sliding properties characteristic of carbon, thus affording improved sliding resistance against sliders composed of high hardness materials. Such DLC films are generally obtained, by DC or RF magnetron sputtering of a carbon target in a gas atmosphere comprising a mixture of Ar gas and a hydrocarbon gas, e.g., methane (CH
4
) or hydrogen (H
2
) gas. The thus-obtained films exhibit DLC properties when a fixed amount of hydrogen is incorporated therein. Incorporation of excessive amounts of hydrogen in the films leads to gradual softening, and thus the hydrogen content of the films must be carefully regulated.
Amorphous, hydrogen-doped, i.e., hydrogenated carbon (a-C:H) films obtained by sputtering of carbon targets in an Ar+H
2
gas mixture and exhibiting diamond-like properties have also been developed for improving the tribological performance of disk drives; however, the electrical insulating properties of such type films lead to undesirable electrical charge build-up or accumulation over time during hard disk operation which can result in contamination, glide noise, etc. In order to solve this problem without sacrifice or diminution of the advantageous mechanical properties of such a-C:H films, attempts have been made to dope or otherwise incorporate nitrogen (N) atoms into the a-C:H films, in view of a substantial decrease in electrical resistivity and optical band gap (E
BG
) exhibited by such N-doped a-C:H films relative to undoped films. In addition to these hydrogen-containing DLC materials, amorphous as well as crystalline DLC films and coatings comprising compounds of carbon and nitrogen (CN
x
) have also been developed and evaluated for use as protective overcoat layers for magnetic recording media.
More recently, protective overcoats comprised of multiple layers of differently constituted carbon-based materials have been developed with the aim of providing magnetic recording media with optimal tribological (e.g., hardness) properties while at the same time providing one or more of good adhesion, low surface energy, reduced stiction, and superior corrosion protection. For example, U.S. Pat. Nos. 5,607,783 and 5,942,317 disclose formation of protective overcoats comprising multiple layers (e.g., 2-3) of C:H, each of the multiple layers having a different amount of hydrogen atoms incorporated
McLeod Paul Stephen
Shows Mark A.
Alejandro-Mulero Luz
Seagate Technology LLC.
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