Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2000-06-22
2002-10-22
Talbot, Brian K. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S129000, C427S130000, C427S282000, C216S022000, C216S041000, C216S052000
Reexamination Certificate
active
06468598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic disks used in hard disk drives, for example, and relates in particular to a method of manufacturing magnetic disks having micro-waviness on its surface or a method for fabricating substrates used for such magnetic disk manufacturing method. Hereinafter, “substrate” refers not only to a base plate itself made of aluminum and glass but also to such substrate including any magnetic, carbon, lubricating or Ni-P layer formed on the base plate.
2. Description of the Related Art
With reference to a conventional layered structure of a magnetic disk shown in
FIG. 24A
, the aluminum substrate material
350
is coated with successive Ni-P layer
352
, magnetic layer
354
and carbon layer
356
. In response to demands for hardness and precision flatness of the substrate in recent years, a glass substrate has become a commercially common replacement for the Al substrate material. As shown in
FIG. 24B
, such a disk is comprised by successive magnetic layer
354
, carbon layer
356
coated on a surface of a glass substrate material
360
.
In order to obtain a high data density, hard disk drives are used by floating a magnetic head on the disk surface at a so-called “semi-contact” state with minimum possible separation distance therefrom, so that a high precision in surface flatness is required on the disk. On the other hand, an excessively flat surface may cause head sticking, and is not desirable. For this reason, it is preferable for the disk surface to have a certain degree of fine roughness, or micro-waviness.
In conventional techniques for aluminum substrates, micro-textured structures are fabricated on a Ni-P layer formed on the substrate surface by using such mechanical methods as abrading with an abrasive tape or abrasive cloth as well as physical treatment such as laser irradiation and bombardment with high energy ions. For glass substrates, texture fabrication techniques include sputtering with hydrofluoric acid vapor or surface crystallization, in addition to laser or high energy ion irradiation.
However, mechanical abrading methods using abrasive tapes and cloths are not suitable for making such high-precision micro-waviness of less than 10 nm height with a variance of less than ±5%, because of limitations due to deviation of abrasive grain size or contact pressure. On the other hand, laser abrasion technique suffers from variations in micro-texture heights, caused by non-uniformity in laser spot size and intensity as well as temporal variations in laser intensity inherent in laser generators. Also, due to its pit-by-pit process, high density texturing (e.g., pit density over 1,000,000 per cm
2
) by laser beam irradiation requires an excessively long exposure time, and the production suffers from high cost and low efficiency due to slowness of the process.
Furthermore, when metals are exposed to an air atmosphere, a natural oxide film layer is formed on the outermost surface. Although the nature of the oxide layer formed varies depending on the material, for Ni-P layer, an oxide layer of about 3~5 nm thickness is formed, causing differences in laser absorption/reflection characteristics for oxidized and non-oxidized surfaces. Laser abrasion texturing is based on a phenomenon of local micro-melting, and because of the differences in melting behavior of the oxidized surface layer and non-oxidized underlayer of Ni-P, such variations are reflected sensitively on the variations in the structure height of micro-waviness produced, and it is virtually impossible to obtain a micro-waviness of an even height. Furthermore, with the laser-texturing process it is difficult to incorporate precision cleaning in the final production step, so that the yield tends to be low.
Regarding the texture fabrication techniques for glass substrate, such as sputtering with hydrofluoric acid vapor, the process is based on local deviation in vapor adsorption ability of the substrate. Therefore, etched depths can vary widely because of non-uniformity in concentration and deviations of duration due to difficulty in controlling the fabrication time. Therefore, non-uniformity increase in surface dissolution depth virtually makes it impossible to produce micro-waviness of a uniform density of less than 10 nm depth over the entire glass substrate.
SUMMARY OF THE INVENTION
Regarding the crystallization method for the glass substrate, non-uniformity in heat treatment, crystal size and degree of precipitation are difficult to control and lead to non-uniformity of surface density and depth of micro-waviness. Therefore, it is difficult to control the depth and density variations to less than 5% over the entire surface of the glass substrate.
Regarding the micro-texturing techniques using high energy ions or plasma particles, fabrication is performed by accelerating the ionic particles in an electrical field and bombarding the substrate surface through a masking pattern for texturing. Such masking patterns should be produced by photolithographic techniques, however, it is difficult to produce ultra-fine line or cavity patterns of less than 1 mm size by using conventional photolithographic techniques. Furthermore, the mask making process suffers from many inherent problems such as the complex nature of the steps, wet cleaning using alcohol and water, and the necessity for subsequent drying and a need for precision drip-sputtering equipment, all of which represent significant barriers to lowering the production cost and improving the productivity.
Techniques such as dissolving particles in alcohol, stirring and dripping onto the substrate to disperse the particles suffer from the problems of aggregation of particles caused by surface tension effects upon solvent evaporation and the resulting variations in local distribution density of particles. In some extreme cases, particles may even contact each other and cause severe local distorbances in particle distribution density.
It is an object of the present invention to provide a method of making a magnetic disk having a uniform textured structure with micro-waviness of fabrication depth of less than 20 nm, preferably less than 10 nm, and a local depth deviation of less than 5%, in which texture patterns are characterized by the fact that lateral surfaces of the structure are sloped or curved.
The object has been achieved in a method for making a magnetic disk having micro-waviness on a fabrication surface of a substrate for reducing dynamic friction and controlling head float. The method includes rotating and irradiating the fabrication surface with a high energy beam from a beam source at an inclined angle to the substrate surface, through a shielding mask having a specific pattern, so as to process a transcription pattern on the substrate surface to produce a textured structure with micro-waviness having sloped or curved side surfaces.
The rate of material removal in a shielded region is slower than that in a region under constant exposure to the beam so that irregularities with sloped or curved side surfaces can be produced by contour transferring, produced by irradiating at an inclined angle or rotating the substrate. Irradiation angle is not particularly limited and can be chosen according to the type of profile desired. To effect uniform material removal over all of the fabrication surface, the beam source should be of a type to radiate an equal amount of energy over the entire fabrication surface. The to obtain a uniform profile of the sloped or curved side surfaces, beam source should produce a beam of high and uniform directionality.
Energy beams may include electron beam, ion beam, laser beam, X-ray beam, fast atomic beam, atomic beam and molecular beam. For example, when fast atomic beam is applied, material suitability and fabrication parameters vary dependent on whether the fabrication surface is a substrate or a coating layer applied on a substrate. Base plate may be divided broadly into two groups: metals and insulators. In the case of metals, disks are t
Hatakeyama Masahiro
Ichiki Katsunori
Ishiguro Juichi
Kunitomo Shinta
Satake Tohru
Ebara Corporation
Talbot Brian K.
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