Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2000-03-31
2002-05-28
Zarabian, Amir (Department: 2924)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C438S690000, C438S756000, C216S097000, C065S030140
Reexamination Certificate
active
06395634
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a glass substrate for use in a magnetic recording medium, such as, a hard disk, a magnetic recording medium having the glass substrate, and a method of manufacturing the magnetic recording medium and the glass substrate.
An interface between a magnetic head and a magnetic disk has become a key technology for improving recording capacity in a technical field for magnetically recording (writing) and reproducing (reading).
It is necessary to excessively reduce a flying height of the magnetic head which is float over a surface of the magnetic disk to improve recording density.
However, when the record/reproduce (write/read) operation is carried out in the known CSS (Contact Start Stop) method, the magnetic head often sticks to the magnetic disk with a low flying height of the magnetic head. Herein, it is to be noted that this phenomenon is generally called “head stiction”.
Suggestions conventionally have been made about a variety of texture techniques to prevent such stiction of the magnetic head. A representative suggestion has been made about a method of forming a surface of an Al/NiP plating substrate into a rough surface by mechanically polishing (mechanically texturing) the surface in Japanese Unexamined Patent Publication (JP-A) No. S62-273619. Further, another suggestion has been made about a method of depositing a thin-film having the rough surface on a glass substrate by the use of the known sputtering process in Japanese Examined Patent Publication (JP-B) No. H04-62413 or a method of forming the rough surface by the use of the chemical etching process in Japanese Examined Patent Publication (JP-B) No. H07-101507, Japanese Examined Patent Publication (JP-B) No. H07-153059 when the glass substrate is superior in flatness in comparison with an aluminum substrate.
In particular, an etching process is carried out by the use of etching liquid after performing a moisture and heat insulation process for a glass substrate in Japanese Examined Patent Publication (JP-B) No. H07-153059. Thereby, repeatability of formation of projections and uniformity of a projection height, which conventionally have caused problems in the texturing technique due to the chemical etching method, have been improved.
Meanwhile, a glide height recently has reached 1.2&mgr; inch or less to improve the recording capacity.
However, the method of forming the texture, which has been conventionally suggested and described above, is the texture technique on the condition that the glide height is equal to about 8&mgr; inch.
Therefore, even when the conventional texture forming method is applied for the recent magnetic disk which records (writes) and reproduces (reads) with the low flying height, it is difficult to obtain the magnetic disk which simultaneously satisfies sufficient electromagnetic conversion characteristic and stiction preventing effect of the magnetic head.
In this case, the conventional glide height was equal to about 8&mgr; inch. Therefore, the surface state (the surface morphology) of the magnetic disk (the substrate) could be sufficiently evaluated by the known thally step. Herein, the surface roughness is measured by scanning a contact needle having radius of several &mgr;m (for example, 2.5 &mgr;m) along the surface.
However, when the flying height becomes 1.2&mgr; inch or less (1 inch=25.4 mm) which is recently required, it is difficult to judge whether or not the surface state of the glass substrate can realize prevention of the stiction of the magnetic head by the use of the conventional thally step.
In the meantime, attention recently has been paid for a magnetic disk apparatus of a load/unload system (a ramp load system) in stead of the CSS system. In such a load/unload system, a magnetic head travels on a data area of the magnetic disk via an arm after the magnetic disk is rotated and is driven different from the CSS system.
Consequently, it is unnecessary to provide the texture for preventing the stiction when the magnetic head halts. Further, the surface roughness of the disk surface becomes small, and the flying height of the magnetic head for the magnetic disk also becomes small. As a result, it is possible to reproduce with high recording density.
Thus, it is required that the medium surface is flat, the projection height is low, and variation of the projection heights is small (values of Rmax/Ra and Rp/Ra are small) in the load/unload system (ramp load system) in comparison with the CSS system.
Specifically, it is necessary that Rmax falls within the range between 3 and 15 nm, Ra falls within the range between 0.2 and 2.5 nm, Rmax/Ra falls within the range between 3 and 15, or Rp falls within the range between 1 and 7 nm, Ra falls within the range between 0.2 and 2.5 nm, and Rp/Ra falls within the range between 1 and 15.
In this case, the surface preferably has projections within the above-mentioned range, and is not completely flat in the load/unload system. In particular, Ra preferably falls within the range between 0.6 and 1.3 nm.
In the meantime, the surface roughness required for the CSS system is specified by Rmax=6-18 nm, Ra=0.7-1.5 nm, and Rmax/Ra=10-20. Further, the surface roughness is specified by Rp=3-15 nm, Ra=0.7-1.5 nm, and Rp/Ra=3-15 when the surface roughness is controlled by Rp.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a magnetic recording medium and a glass substrate for the magnetic recording medium which is capable of realizing a glide height of 1.2&mgr; inch or less and which is capable of realizing high electromagnetic characteristic.
It is another object of this invention to provide a magnetic recording medium and a glass substrate for the magnetic recording medium which is suitable for a load/unload system by controlling a projection height, projection density, variation of projection heights, and variation of projections and which has high CSS durability characteristic suitable for a CSS system.
Inventors have paid attention to specify the surface state of the glass substrate by the use of the interatomic force microscope (AFM) in order to evaluate the surface state of the glass substrate. This is because it is impossible to identify whether or not the surface state of the glass substrate is suitable, since the resolution is low in the conventional measuring method using the contact needle method.
Based upon the above-mentioned evaluation method, it has been confirmed that height and distribution (namely, variation of the height) of each projection of fine roughness, which are formed on a principle surface of the glass substrate, are important factors to achieve the above purpose.
Further, as a result of various experiments, it has been found out that the glass substrate surface as a target or a goal can not be obtained unless specific polishing condition and surface process condition are properly combined. This invention is performed based upon this analyzed result.
Specifically, inventors have discovered that the trace, along which the abrasive grain passes, tends to be formed as the island (peak) when the surface is processed by the hydrosilicofluoric acid (which may be referred to as hydrofluosilic acid or hexafluorosilicic acid) after polishing by the polishing material containing the free abrasive grain.
Although this mechanism is not clear, the load in the polishing step by the free abrasive grain is applied to the surface of the glass substrate. Consequently, the network of Si—O is (systematically and) structurally changed, and nonuniformity occurs in the remaining stress distribution by the structural change.
As a result, the etching rate due to the hydrosilicofluoric acid becomes slow in the portion having relatively high remaining distortion (namely, a trace portion along which the free agrasive grain passes). This is assumed to be the above-mentioned mechanism.
An application is previously filed on the basis of this analyzed result in Japanese Patent Application No. H10-233261.
It has been found out
Hoya Corporation
Pyonin Adam
Zarabian Amir
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