Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2002-03-25
2004-11-23
Pham, Long (Department: 2814)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C216S022000, C216S097000
Reexamination Certificate
active
06821893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for information recording media and a manufacturing method thereof, and more specifically to a substrate for information recording media used in information recording apparatuses such as hard disk drives and a manufacturing method thereof.
2. Prior Art
In recent years, there has been remarkable progress in information technology, and development of various types of information recording apparatus for storing information has been carried out with vigor. Hard disk drives (hereinafter referred to as “HDDs”) form the mainstream of such information recording apparatuses.
In an HDD, recording and playback of information are carried out by means of a magnetic head flying over a data zone formed on a magnetic disk substrate. Driving methods used include a CSS (contact start/stop) method and a ramp load method.
In the CSS method, a CSS zone in which uniform minute undulations of height several tens of nm are formed is provided along the inner periphery or the outer periphery of the magnetic disk substrate. The magnetic head flies over the data zone of the magnetic disk substrate while the magnetic disk substrate is rotating, and slides over the CSS zone of the magnetic disk substrate when the magnetic disk substrate stops or starts up.
In the ramp load method, the magnetic head flies over the magnetic disk substrate while the magnetic disk substrate is rotating, and is stored in a predetermined storage position when the magnetic disk substrate stops.
In both the CSS method and the ramp load method, while the magnetic disk substrate is rotating, the magnetic head is thus raised up slightly from the magnetic disk substrate, and flies over the surface of the magnetic disk substrate with a gap (hereinafter referred to as the “flying height”) of several tens of nm maintained between the magnetic head and the surface of the magnetic disk substrate.
In an HDD, it is necessary to prevent the magnetic head from contacting the magnetic disk substrate while flying over the magnetic disk substrate, thus preventing the magnetic head from being subjected to excessive resistance. To this purpose, art has been known from hitherto in which precision polishing is carried out using a polishing agent containing loose abrasive grains of mean grain diameter in a range of 0.3 &mgr;m to 3.0 &mgr;m, and then etching is carried out using silicofluoric acid, thus forming a large number of minute projections referred to collectively as “texture” on the surfaces of the magnetic disk substrate (Japanese Laid-open Patent Publication (Kokai) No. 2000-132829).
According to this prior art, upon etching the surfaces of the magnetic disk substrate with silicofluoric acid, polishing marks (abrasive marks) formed by the polishing agent during the precision polishing remain behind as projections, and hence a texture comprised of a large number of minute projections is formed on the surfaces of the magnetic disk substrate. Moreover, silicofluoric acid gives a slower etching rate and weaker etching than hydrofluoric acid or an aqueous solution of hydrofluoric acid containing potassium fluoride, and hence the surface roughness can be controlled to high accuracy.
Moving on, as the amount of information stored has increased enormously in recent years, there have been calls for HDDs that are small but have a large storage capacity. It has thus become necessary to increase the recording density of the data zone, and hence there have been calls to reduce the flying height (for example to 10 nm or less) to cope with this increase in the recording density of the data zone.
However, if the flying height is reduced, then the air layer between the magnetic head and the magnetic disk becomes thinner, and hence the floating stability of the magnetic head drops.
To reduce the flying height while maintaining stability, it is necessary not only to completely remove minute particles of foreign matter attached to the magnetic disk substrate so that the magnetic head will not collide with such foreign matter, but also improve the quality of the texture, thus improving the floating stability of the magnetic head. It is thus necessary to reduce the projection height of the minute projections as much as possible but increase the density of the minute projections, and moreover suppress variation in the projection height.
However, according to the prior art described above, even though the precision polishing is carried out using a polishing agent containing loose abrasive grains of mean grain diameter in a range of 0.3 &mgr;m to 3 &mgr;m, because the etching rate given by silicofluoric acid is low, abnormal linear or point-like projections having a large projection height are formed through the etching carried out after the polishing. As a result, there is a problem that if a magnetic disk manufactured from the magnetic disk substrate is driven with a flying height of 10 nm or less as described above, then there will be a risk of the magnetic head colliding with the abnormal projections, resulting in so-called head crashes or thermal asperity.
Moreover, according to the prior art described above, the maximum permitted value of the surface roughness Ra is 2.5 nm, and hence there is a problem of not being able to completely deal with the issue of the floating stability of the magnetic head at low flying height.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide a substrate for information recording media and a manufacturing method thereof, which allow an information recording medium to be driven reliably and stably even when the flying height is made lower than conventionally to cope with increased recording density of the data zone.
It is envisaged that, in the technical field of information recording media, in the future there will be calls to further increase the data zone recording density. To realize such an increase in the data zone recording density, it will be necessary to further reduce the flying height as described above, and hence to further reduce the projection height of the minute projections formed on the substrate surfaces.
One might think that to reduce the height of the minute projections, the depth of etching from the substrate surfaces should be reduced. However, if the depth of etching is reduced, then most of the compressed layers (polishing marks) formed through the polishing will remain, i.e. it will not be possible to remove the compressed layers sufficiently. As a result, when the substrate for information recording media is exposed to a high temperature during chemical strengthening treatment, sputtering or the like carried out after the minute projections have been formed, relaxation expansion will be brought about by the heat, and hence the minute projections will grow. Abnormal projections having a large projection height will thus arise, and hence there will be a risk of a magnetic head colliding with these abnormal projections and thus thermal asperity or head crashes occurring.
To obtain a desired floating stability suitable for reducing the flying height, it is thus necessary to reduce the projection height of the minute projections, and also suppress variation in the projection height which can occur due to relaxation expansion as described above. Specifically, to avoid the formation of abnormal projections having a large projection height, it is thought to be necessary to make the etching depth as large as possible and thus sufficiently remove the compressed layers.
The present inventors carried out assiduous studies from such a perspective, and as a result discovered that by adding an alkaline compound to hydrofluoric acid to produce an acidic solution containing a fluoride salt, and carrying out surface treatment on a substrate with this acidic solution, the surface roughness Ra of the substrate surfaces can be reduced reliably and the projection height can be kept down and made uniform; moreover, even upon subsequently carrying out heat treatment such as chemi
Kurachi Junji
Mitani Kazuishi
Saito Yasuhiro
Frishauf Holtz Goodman & Chick P.C.
Hoya Corporation
Peralta Ginette
Pham Long
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