Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-07-17
2003-03-11
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S234300, C029S603120, C029S603150, C216S066000, C219S121680
Reexamination Certificate
active
06532132
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for marking a sintered product with identification information while minimizing the generation of contamination. The present invention also relates to a method for fabricating a substrate for a magnetic head including the marking step, a sintered product with identification information marked thereon, a magnetic head, and a storage medium drive.
In recent years, thin film magnetic heads of various constructions have been used as magnetic head sliders for hard disk drives (HDD), tape storages, floppy disk drives (FDD), and the like. Sintered substrates, made of compositions such as Al
2
O
3
—TiC, SiC, and ZrO
2
, are used for such thin film magnetic heads.
FIG. 1A
illustrates a typical thin film magnetic head slider
10
. The magnetic head slider
10
has two side rails
11
on the track side thereof facing the surface of a magnetic disk. The surface of the magnetic head slider
10
where the side rails
11
are formed is sometimes called an air bearing surface (ABS). When the magnetic disk is rotated at high speed with a motor or the like, in the state where the side rails
11
of the magnetic head slider
10
lightly press the surface of the magnetic disk under head suspension, a layer of air formed on the surface of the magnetic disk intrudes into a gap under the air bearing surface of the slider
10
. This causes the magnetic head slider
10
to be slightly lifted. In this way, the magnetic head slider
10
hovers near the surface of the magnetic disk, to effect recording/reproducing operation.
Thin films
12
are formed on one end face of the magnetic head slider
10
for magnetic interaction with a storage medium such as the magnetic disk. The thin films
12
constitute an electric/magnetic transducer element. On the other end face of the magnetic head slider
10
, identification information
13
, such as a serial number, is engraved. Methods for engraving the identification information
13
on the sintered substrate are disclosed in Japanese Laid-Open Patent Publication No. 9-81922, No. 10-134317, and No. 11-126311, for example.
The magnetic head slider
10
is obtained in the following manner. A bar
20
as shown in
FIG. 1B
is cut from a sintered substrate
1
as shown in
FIG. 1C
, and the bar
20
is divided into a plurality of chips. The positional relationship between the sintered substrate
1
shown in FIG.
1
C and the magnetic head slider
10
shown in
FIG. 1A
is such that an end face
4
of the sintered substrate
1
is parallel with the air bearing surface of the magnetic head slider
10
.
As the size of thin film magnetic heads
12
is reduced to cope with the reduction in size and weight of electronic apparatuses, the thickness of the sintered substrate
1
(corresponding to the length L of the magnetic head slider
10
) is reduced, and the thickness T of the bar
20
(corresponding to the height of the magnetic head slider
10
) is reduced. For example, in a magnetic head slider called a pico-slider, L is about 1.2 mm and T is about 0.3 mm. With such a short magnetic head slider, the size of characters to be engraved thereon should also be made smaller.
A laser marking method is commonly used for engraving (hereinafter, also called “inscription” and “marking”) of the identification information
13
. According to the laser marking method, the identification information
13
shown in
FIGS. 1A and 1B
is inscribed on the back surface
3
of the substrate
1
in the wafer state before being divided into the bars
20
. Subsequently, various thin films
12
are formed on the opposite surface
2
of the substrate
1
.
The conventional laser marking method will be described with reference to FIG.
2
. The back surface
3
of the sintered substrate
1
is irradiated with a laser beam
6
converged by a lens
5
. An irradiated portion of the substrate
1
is rapidly heated and evaporated, so that a small concave portion or recessed portion is formed on the back surface
3
of the substrate
1
. At this time, pieces of the sintered material constituting the substrate
1
scatter. Some of these pieces fall back on the substrate
1
. By scanning the back surface
3
of the substrate
1
with the laser beam
6
, an arbitrary recess pattern can be formed. Thus, by forming a pattern of alphabets, numerals, barcodes, and the like, various types of identification information can be written at arbitrary positions on the substrate
1
.
There are problems associated with the conventional laser marking method. First, debris is generated by the laser light irradiation. This debris often causes contamination in later fabrication process steps, by becoming absorbed and accumulated in inscribed grooves and the like. Second, burrs are generated at edges of the grooves during the laser light irradiation. Therefore, an additional step for removing such burrs is required.
FIG. 3A
schematically illustrates the cross-section of the sintered substrate
1
after the substrate
1
has been engraved by the conventional laser marking method. This cross-sectional view was drawn based on a photograph taken with a scanning electron microscope (SEM). Referring to
FIG. 3A
, a deep concave portion
30
is formed on the surface of the substrate
1
by irradiation with laser light. The depth of the concave portion
30
, measured from the back surface of the substrate
1
in the direction shown by the arrow a, is 30 to 50 &mgr;m. A convex portion (burr)
31
is formed along the edge of the concave portion
30
. The height of the burr
31
measured in the direction shown by the arrow b is of the order of several micrometers. The width of the concave portion
30
is of the order of 20 &mgr;m, for example. Hereinafter, the depth of the concave portion is referred to as the “inscription depth”, and the height of the raised portion around the concave portion is referred to as the “edge burr height”.
A number of particles
32
attach to the wall of the deep concave portion
30
formed by the laser light irradiation. The particles
32
are not necessarily in the form of particles, but are herein called “particles” for simplification. In order to remove the particles
32
from the substrate
1
, a long-duration cleaning step, such as ultrasonic cleaning, is required after the marking step. Even by this cleaning step, however, it is difficult to remove the particles
32
located deep inside the concave portion
30
to a sufficient degree.
If a large number of particles
32
are generated during the laser marking step, part of the particles
32
may be dispersed in a cleaning solution, and part of the particles
32
in the cleaning solution may possibly re-attach to the surface of the substrate
1
that has not been irradiated with laser light (surface
2
). If this re-attachment occurs and an insulating thin film made of amorphous aluminum oxide or the like is deposited on the surface
2
of the substrate
1
, the particles
32
may be included in the insulating thin film. The surface of the insulating thin film is smoothed before a magnetic thin film is deposited thereon. Therefore, if the particles
32
exist in the insulating thin film, the insulating thin film may be locally peeled off together with the particles
32
, resulting in formation of pinholes in the insulating thin film. Even if formation of pinholes is evaded, the insulating thin film may be substantially thinned in some portions due to the existence of the particles
32
. The insulating property of such portions of the insulating thin film is decreased. Such inclusion of the particles in the insulating thin film does not necessarily occur. However, as long as the inscribed portions of the back surface of the substrate serve as a dust source, the yield may be lowered in the subsequent steps, and also the reliability of the final products may be decreased.
In order to improve the production yield of thin film magnetic heads, the quality of the insulating film deposited on the sintered substrate
1
should preferably be improved as much as possible. In order to achieve t
Morikawa Takayuki
Tsujimoto Shinji
Costellia Jeffrey L.
Sumitomo Special Metals Co. Ltd.
Tupper Robert S.
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