Chemistry: electrical and wave energy – Processes and products – Vacuum arc discharge coating
Reexamination Certificate
2002-06-13
2004-02-10
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Vacuum arc discharge coating
C204S192150, C204S192200, C204S298120, C204S298180, C204S298210, C204S298220
Reexamination Certificate
active
06689253
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for forming high quality sputtered films on a substrate surface, e.g., a disk-shaped substrate, which method and apparatus utilize a magnetically enhanced facing target assembly. The invention has particular utility in the manufacture of disk-shaped, thin-film magnetic and magneto-optical (MO) recording media.
BACKGROUND OF THE INVENTION
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon-based material having good mechanical (i.e., tribological) properties. A similar situation exists with MO media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional manufacturing methodology, a majority of the above-described layers constituting multi-layer magnetic and/or MO recording media are deposited by cathode sputtering, typically by direct current (DC) sputtering utilizing a magnetically enhanced, facing target sputtering apparatus, such as illustrated in
FIG. 1
in schematic, simplified cross-sectional view. As shown in the figure, such conventionally configured, magnetically enhanced facing target sputtering apparatus comprises a pair of spaced-apart, planar targets (cathodes) with their respective sputtering (front) surfaces in facing relation, with a respective annular-shaped magnet extending around the rear peripheral edge of each target for providing a magnetic field extending perpendicularly to the sputtering surfaces. During operation, the perpendicular magnetic field serves to confine the plasma which is generated to a zone within the inter-target space, as indicated by the dashed line in the figure. A substrate, illustratively a disk-shaped substrate, is positioned as shown, i.e., outside of the plasma zone, in order to effect damage-free, low roughness (i.e., smooth) film deposition on the substrate surface facing the plasma zone. Placement of the substrate exteriorly of the plasma zone also serves to minimize the frequency or number of film defects, such as may result from various phenomena, e.g., arcing, which may occur between the facing targets. However, conventional magnetically enhanced, facing target sputtering apparatus, such as shown in
FIG. 1
, are unsuitable for manufacturing high areal recording density magnetic media, e.g., perpebndicular and anti-ferromagnetically coupled (AFC) media, because good film uniformity over the entire substrate (i.e., disk) surface is not achievable unless the targets are extremely large, relative to the substrate.
In general, conventional magnetically enhanced sputtering methods and apparatus, e.g., DC magnetron sputtering methods and apparatus, incur four major deficiencies when utilized in the manufacture of thin film magnetic and magneto-optical (MO) recording media, which deficiencies are:
1. high micro-roughness at interfaces between adjacent thin films;
2. high frequency of film defects arising from arcing between facing targets, target flaking, and shield flaking;
3. poor thickness uniformity across the disk diameter; and
4. poor stability and repeatability when depositing ultra-thin films.
More specifically, in the manufacture of thin film, multi-layered magnetic and MO recording media, roughness at the interface between adjacent thin film layers exerts a significant influence on lattice matching between the adjacent layers; film stress and strain; formation of defects, such as stacking faults, etc., which factors ultimately determine the performance properties or characteristics of the media.
In particular, interfacial roughness is a very critical factor in the performance of anti-ferromagnetically coupled (AFC) media, wherein a very thin non-magnetic spacer layer, e.g., of ruthenium (Ru), only several atom layers thick, is formed between adjacent ferromagnetic layers. Since the interfacial roughness of multi-layer thin film structures produced by conventional sputtering techniques is rather high, the coupling coefficient J of such AFC media is much lower than that which is predicted from theory, which phenomena severely limits the applicability/utility of such media.
Roughness of conventional magnetron sputtered films is typically related to bombardment of the substrate by electrons and/or other negatively charged particles during the sputter deposition process, since the substrate is immersed in, or closely adjacent to, the plasma zone. The greater the bombardment, the greater the roughness. In addition, interaction between the substrate and the plasma arising from the relative positioning of the former and the latter can disadvantageously result in significant loss of manufacturing (i.e., product) yield in mass production. However, as indicated supra, conventional magnetically enhanced, facing target sputtering apparatus, wherein the substrate(s) is (are) positioned outside of the intense plasma zone or region, such as the facing target sputtering apparatus shown in
FIG. 1
, are unsuitable for manufacturing high areal recording density magnetic media, e.g., perpendicular and anti-ferromagnetically coupled (AFC) media, because good film uniformity over the entire substrate (i.e., disk) surface is not achievable unless the targets are extremely large, relative to the substrate. However, the use of large target sputtering apparatus incurs several significant disadvantages including, inter alia, increased sputtering station size, target power and pumping requirements, and substantially increased target material costs.
Accordingly, there exists a need for improved means and methodology for depositing, by sputtering techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, defect-free thin films of high purity and with low interfacial roughness and good film thickness uniformity, suitable for use in high areal recording density, multi-layer magnetic recording media, such as hard disks. More specifically, there exists a need for means and methodology which overcome the above-mentioned drawbacks and disadvantages associated with conventional facing target sputtering means and methodology when utilized in the manufacture of single- and/or dual-sided magnetic and/or MO recording media, as in the form of hard disks, or in the manufacture of various other products and manufactures comprising at least one thin film layer.
The present invention addresses and solves the above-described problems and drawbacks associated with the use of conventional facing target sputtering means and methodology when utilized in the manufacture of high quality multi-layer film structures and recording media, notably the requirement for extremely large target sizes, while maintaining full capability with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various devices and articles requiring high quality,
Cheng Yuanda Randy
Koh Chinsoon
Sawasaki Stephen Hiroshi
Shi Jianzhong
McDonald Rodney G.
Seagate Technology LLC
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