Single disc vapor lubrication

Details Single disc vapor lubrication Single disc vapor lubrication

2001-03-06

2003-09-02

Beck, Shrive P. (Department: 1763)

Coating apparatus

Gas or vapor deposition

Crucible or evaporator structure

C118S726000, C118S719000, C118S720000, C118S730000

Reexamination Certificate

active

06613151

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an apparatus and method for uniformly applying a thin film of a lubricant to the substrate surfaces in a solventless manner. The invention has particular utility in the manufacture of magnetic or magneto-optical (“MO”) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of layers formed on a suitable substrate, e.g., a disc-shaped substrate, wherein a thin lubricant topcoat is applied to the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducers operating at very low flying heights.
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., disc form, such as utilized in computer-related applications, comprises a non-magnetic disc-shaped 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 or laminate 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 (C)-based material having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate 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 transparent dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disc form, such as described supra, are typically lubricated with a thin film of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out heads/transducers operating at low flying heights, as in a hard disk system functioning in a contact start-stop (“CSS”) mode. Conventionally, a thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether. However, a drawback inherent in such dipping process is the consumption of large quantities of solvent, resulting in increased manufacturing cost and concern with environmental hazards associated with the presence of toxic or otherwise potentially harmful solvent vapors in the workplace.
Another drawback associated with the conventional dipping method for applying a thin film of a polymeric lubricant to a substrate results from the lubricant materials being mixtures of long chain polymers, with a distribution of molecular weights. Since the molecular weight of the polymeric lubricant affects the mechanical (i.e., tribological) performance of the head-disc interface, it is common practice to subject the polymeric lubricant mixtures (as supplied by the manufacturer) to a fractionation process prior to adding the lubricant to the solvent in order to obtain a fraction having a desired molecular weight distribution providing optimal tribological performance. However, such pre-fractionation undesirably adds an additional step and increases the overall process cost.
Vapor deposition of thin film lubricants is an attractive alternative to dip lubrication in view of the above drawbacks. Specifically, vapor deposition of lubricant films is advantageous in that it is a solventless process and the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step. Moreover, vapor deposition techniques can provide up to about 100% bonded lubricant molecules when utilized with appropriate polymeric lubricants and magnetic and/or MO disc substrates having deposition surfaces comprised of a freshly-deposited carbon-based protective overcoat layer.
However, existing vapor deposition apparatus (e.g., Intevac VLS 100, Intevac Corp., Santa Clara, Calif.) for applying a thin layer of polymeric lubricant to a thin film data/information storage and retrieval medium, e.g., in disc form, utilize a static process/system, wherein a disc-shaped substrate is moved to a position facing the front (i.e., orifice) of a source of lubricant vapor (e.g., by means of a disc lifter) and statically maintained at that position while the lubricant film is deposited on the entire disc surface, with the lubricant film thickness being determined (i.e., controlled) by the length of the interval during which the disc surface is statically maintained facing the orifice(s) of the lubricant vapor source.
In order to control the spatial distribution, hence thickness uniformity, of the lubricant thin films obtained with such static vapor deposition process/apparatus at deposition rates of from about 1 to about 10 Å/sec. for providing lubricant film thicknesses up to about 50 Å, a diffuser plate for the lubricant vapor is provided intermediate the lubricant vapor source and the substrate surface, thereby adding to the system complexity and necessitating periodic maintenance of the diffuser plate for ensuring clear vapor passage through each of the openings in the diffuser plate. In addition, such static vapor lubrication systems incur a drawback when utilized as part of an in-line or similar type multi-chamber or modular system for manufacturing magnetic or MO media, in that a line-of-sight path is required for the mechanism utilized for positioning the disk surface opposite the lubricant vapor source. As a result, a path can be established for the lubricant vapor to escape from the lubricant deposition chamber into adjacent process chambers utilized for different processing functions and result in their being contaminated with lubricant vapor.
Notwithstanding the improvement in spatial uniformity of lubricant film thickness afforded by the use of a diffuser plate or similar element between the lubricant vapor source and the disk substrate surface, current vapor deposition processes for applying thin films of lubricant or other additive to substrate surfaces result in some degree of film thickness non-uniformity. It is believed that such spatial non-uniformity has dual origins, as follows:
(1) although the above-described system is nominally static, the substrate (e.g., a disc) is necessarily in motion during its placement facing the lubricant vapor source and during its removal therefrom, which motion creates a non-uniformity, i.e., a thickness gradient, across the disc surface in the direction of the motion. The extent and magnitude of the gradient is a function of the deposition rate and the speed of the mechanism utilized for placement of the disc in facing relation to the lubricant vapor source and removal therefrom; and
(2) because of the large substrate size (i.e., disc diameter) and physical constraints on apparatus dimensions, multiple lubricant vapor sources and/or vapor diffuser plates generally are necessary for obtaining thickness uniformity over the entire substrate surface. However, even in the best cases wherein multiple lubricant vapor sources and/or vapor diffuser plates are utilized, regions of greater and lesser lubricant or additive thickness are routinely obtained.
In view of the above, there exists a clear need for imp

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